This First Article of a 12-Part Series on Equine Anatomy and Physiology

Home , Back (horse), Equine anatomy, Fetlock, Hock (anatomy), Lameness (equine)

By Les seLLnow he evolution of the horse from a tiny, four-toed an imal, T perhaps no more than one foot tall, to the variety of equines in existence today, is one of the wonders of nature. During that process of change, the horse evolved over many thousands of years from an animal that predators hunted for food to an animal that became a servant and friend for mankind. Today’s horses are designed to do one of two things— pull a load with their shoulders or carry riders on their backs. The type of horses utilized for these respective tasks varies a good deal; one is large and pon d erous and the other is lighter-boned with less mu s cle mass. Even within these two types, there are significant differences. For example, the conformation of a roping or cutting This first article of a 12-part series on equine anatomy and horse is different from that of the American Saddle- physiology discusses basic terminology, the horse’s largest bred. Yet there is a basic sameness to anatomy. organ, and how horses and humans are alike (and different) Dr. roBin Peterson iLLustration

2 www.TheHorse.com The horse DecemberJanuary 2006 DecemberJanuary 2006 2006 The horse www.TheHorse.com 3 By Les seLLnow he evolution of the horse from a tiny, four-toed an imal, T perhaps no more than one foot tall, to the variety of equines in existence today, is one of the wonders of nature. During that process of change, the horse evolved over many thousands of years from an animal that predators hunted for food to an animal that became a servant and friend for mankind. Today’s horses are designed to do one of two things— pull a load with their shoulders or carry riders on their backs. The type of horses utilized for these respective tasks varies a good deal; one is large and pon d erous and the other is lighter-boned with less mu s cle mass. Even within these two types, there are significant differences. For example, the conformation of a roping or cutting This first article of a 12-part series on equine anatomy and horse is different from that of the American Saddle- physiology discusses basic terminology, the horse’s largest bred. Yet there is a basic sameness to anatomy. organ, and how horses and humans are alike (and different) Dr. roBin Peterson iLLustration

2 www.TheHorse.com The horse DecemberJanuary 2006 DecemberJanuary 2006 2006 The horse www.TheHorse.com 3 explanation of terminology that is routine horse’s back is caudal to his neck. for veterinarians and researchers, but can rostral—That part of the structure MembershipMembership be confusing to some horse owners. Along located closer to the nose (rostrum). Ex- with the two authors’ terminology, we’ll add ample: The eyes are rostral to the ears. examples to dem onstrate how the termi- Proximal—A location toward the at- nology might be employed. Understanding tached end of a limb. Example: The proxi- the terminology is essential when discuss- mal end of the cannon bone connects with HasHas ItsIts Benefits!Benefits! In this opening article of our 12-part ing various conditions with a veterinarian. the knee. series on equine anat omy and physiology, Here is some terminology, accompanied Distal—Indicates a location toward the we will attempt to paint a picture of how by illustrations, to help you visualize: free end of a limb—the part that is farther Become A Member of the American Association of today’s horse is constructed and what this on side—The horse’s left side; also called away from the body. Example: The distal means in the realm of form to function. We near side. Example: Normally, the side on end of the cannon bone connects with the Equine Veterinary Technicians and Enjoy These Bene ts: will not be quoting a lot of sources, for the which we mount and dismount. long pastern bone or third phalanx. most part, because the information to be off side—Right side of the horse; also Median Plane—This divides the horse’s presented is an amalgamation of what has called far side. Example: One theory of why body into right and left halves (median • Quarterly newsletter • Member eligibility to of ce positions on the been recorded in thousands of scientific pa- we mount from the left instead of the right means in the middle). • Advance noti cation of regional CE events executive board, on equine specialty pers, textbooks, and manuals as knowledge is that warriors and soldiers of old gener- sagittal Plane—Any plane parallel to the • Access to member-only section of web site which academy, or the equine certi cate program has been gained and disseminated through ally carried a sword on the left side and this median plane. Example: A plane dividing the years. However, we would be remiss in would get in the way if swinging up from the right and left sides of a hoof. features an employment database and • Purchasing power offered through NTRA and not calling attention to two valuable sourc- the right or off side of the horse. Medial—Structures located closer to the CE announcements Blackwell Publishing es upon which we shall draw heavily. Both Dorsal—Parts of the horse’s anatomy median plane. Example: When you look at • Reduced registration fees at the annual AAEP/ • Representation at veterinary conferences are written at the layman level. They are toward his back (dorsum). Ex ample: The a horse’s left side, you see the medial sur- • Technician networking Horses and Horsemanship by the late M.E. point of the croup is dorsal to the stifle. faces of his right limbs. AAEVT meeting and regional AAEVT meetings Ensminger, BS, MA, PhD, and The Coloring Ventral—Anatomy toward the belly (ven- Lateral—Structures located away from • Member discounts at CE events, on books/publica- • Public, industry and professional awareness Atlas of Horse Anatomy by Robert A. Kain- ter). Example: The stallion’s reproductive the median plane. Example: When you tions, and on membership renewal • Speaking opportunities er, DVM, MS, and Thomas O. McCracken, organs are ventral to his flank. look at a horse’s left side, you see the lateral • On-line CE courses MS, both of whom were at Colorado State Cranial—That part of the horse’s struc- surfaces of his left limbs. University. ture above the knees and hocks located Transverse Plane—Passes through the McCracken, who resigned from Colora- closer to the skull (cranium). Example: The head, trunk, or limb perpendicular to the do State in 1994 to enter private business, withers are cranial to the tail. part’s long axis. Example: An ultrasound has authored seven books, and today he Caudal—That part of the horse’s struc- image gives a transverse view of the limb. is president of Biographix, LLC. Early in ture above the knees and hocks located Dorsal Plane—Passes through a body his career, McCracken spent two years in closer to the tail (cauda). Example: The part parallel to its dorsal surfaces. Saudi Arabia as chief medical illustrator for the King Faisal Specialist Hospital and Research Center in Riyadh. Through the years, he has received many honors and awards of excellence for his work. Kainer joined the anatomy faculty at Colorado State in 1961 and remained there The American Association of Equine Veterinary Technicians & Assistants (AAEVT) for 27 years. He, too, has won a variety of is a sister organization to the American Association of Equine Practitioners (AAEP). awards and honors for his work. Needless to say, since there are entire We are a separate, non-pro t corporation whose membership consists of technicians, assistants, books written on equid anatomy and physiology, it would be impossible to address practice managers and support staff from all aspects of equine veterinary medicine. the entire animal in one article. Therefore, this month we look in-depth at the horse’s Our mission is to promote the health and welfare of the horse largest organ, its skin, and details of the through the education and professional enrichment nomenclature used to discuss anatomy and physiology, as well as lightly touch on ustration of the equine veterinary technician and assistant. LL structures that will be covered in-depth in the coming year. In the months ahead Membership is open to all technicians, assistants, practice we’ll have articles on joints, the foreleg, the managers and paraprofessionals in the United States and Canada, hind limb, the hoof, the head and neck, the back, muscles, tendons and ligaments, and in Peterson i regardless of licensure or certi cation. Student membership is open to B the digestive, circulatory, respiratory, and o those enrolled in AVMA accredited veterinary technology schools. r reproductive systems. As of 2007, international membership is also available. Dr. There are some similarities between human and equine anatomy, but there are a great many differ- A Glossary to Get You Started ences as well. For example, the human knee and the equine stifle have a lot in common. The equine We will begin this discussion of equine radius is similar to the human forearm. The equine carpal or knee bones are similar to human wrist For more information and to become a member, anatomy with Kainer’s and McCracken’s bones. And the equine splint bones compare to human fingers. please visit our web site at www.aaevt.org 4 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 5 explanation of terminology that is routine horse’s back is caudal to his neck. for veterinarians and researchers, but can rostral—That part of the structure MembershipMembership be confusing to some horse owners. Along located closer to the nose (rostrum). Ex- with the two authors’ terminology, we’ll add ample: The eyes are rostral to the ears. examples to dem onstrate how the termi- Proximal—A location toward the at- nology might be employed. Understanding tached end of a limb. Example: The proxi- the terminology is essential when discuss- mal end of the cannon bone connects with HasHas ItsIts Benefits!Benefits! In this opening article of our 12-part ing various conditions with a veterinarian. the knee. series on equine anat omy and physiology, Here is some terminology, accompanied Distal—Indicates a location toward the we will attempt to paint a picture of how by illustrations, to help you visualize: free end of a limb—the part that is farther Become A Member of the American Association of today’s horse is constructed and what this on side—The horse’s left side; also called away from the body. Example: The distal means in the realm of form to function. We near side. Example: Normally, the side on end of the cannon bone connects with the Equine Veterinary Technicians and Enjoy These Bene ts: will not be quoting a lot of sources, for the which we mount and dismount. long pastern bone or third phalanx. most part, because the information to be off side—Right side of the horse; also Median Plane—This divides the horse’s presented is an amalgamation of what has called far side. Example: One theory of why body into right and left halves (median • Quarterly newsletter • Member eligibility to of ce positions on the been recorded in thousands of scientific pa- we mount from the left instead of the right means in the middle). • Advance noti cation of regional CE events executive board, on equine specialty pers, textbooks, and manuals as knowledge is that warriors and soldiers of old gener- sagittal Plane—Any plane parallel to the • Access to member-only section of web site which academy, or the equine certi cate program has been gained and disseminated through ally carried a sword on the left side and this median plane. Example: A plane dividing the years. However, we would be remiss in would get in the way if swinging up from the right and left sides of a hoof. features an employment database and • Purchasing power offered through NTRA and not calling attention to two valuable sourc- the right or off side of the horse. Medial—Structures located closer to the CE announcements Blackwell Publishing es upon which we shall draw heavily. Both Dorsal—Parts of the horse’s anatomy median plane. Example: When you look at • Reduced registration fees at the annual AAEP/ • Representation at veterinary conferences are written at the layman level. They are toward his back (dorsum). Ex ample: The a horse’s left side, you see the medial sur- • Technician networking Horses and Horsemanship by the late M.E. point of the croup is dorsal to the stifle. faces of his right limbs. AAEVT meeting and regional AAEVT meetings Ensminger, BS, MA, PhD, and The Coloring Ventral—Anatomy toward the belly (ven- Lateral—Structures located away from • Member discounts at CE events, on books/publica- • Public, industry and professional awareness Atlas of Horse Anatomy by Robert A. Kain- ter). Example: The stallion’s reproductive the median plane. Example: When you tions, and on membership renewal • Speaking opportunities er, DVM, MS, and Thomas O. McCracken, organs are ventral to his flank. look at a horse’s left side, you see the lateral • On-line CE courses MS, both of whom were at Colorado State Cranial—That part of the horse’s struc- surfaces of his left limbs. University. ture above the knees and hocks located Transverse Plane—Passes through the McCracken, who resigned from Colora- closer to the skull (cranium). Example: The head, trunk, or limb perpendicular to the do State in 1994 to enter private business, withers are cranial to the tail. part’s long axis. Example: An ultrasound has authored seven books, and today he Caudal—That part of the horse’s struc- image gives a transverse view of the limb. is president of Biographix, LLC. Early in ture above the knees and hocks located Dorsal Plane—Passes through a body his career, McCracken spent two years in closer to the tail (cauda). Example: The part parallel to its dorsal surfaces. Saudi Arabia as chief medical illustrator for the King Faisal Specialist Hospital and Research Center in Riyadh. Through the years, he has received many honors and awards of excellence for his work. Kainer joined the anatomy faculty at Colorado State in 1961 and remained there The American Association of Equine Veterinary Technicians & Assistants (AAEVT) for 27 years. He, too, has won a variety of is a sister organization to the American Association of Equine Practitioners (AAEP). awards and honors for his work. Needless to say, since there are entire We are a separate, non-pro t corporation whose membership consists of technicians, assistants, books written on equid anatomy and physiology, it would be impossible to address practice managers and support staff from all aspects of equine veterinary medicine. the entire animal in one article. Therefore, this month we look in-depth at the horse’s Our mission is to promote the health and welfare of the horse largest organ, its skin, and details of the through the education and professional enrichment nomenclature used to discuss anatomy and physiology, as well as lightly touch on ustration of the equine veterinary technician and assistant. LL structures that will be covered in-depth in the coming year. In the months ahead Membership is open to all technicians, assistants, practice we’ll have articles on joints, the foreleg, the managers and paraprofessionals in the United States and Canada, hind limb, the hoof, the head and neck, the back, muscles, tendons and ligaments, and in Peterson i regardless of licensure or certi cation. Student membership is open to B the digestive, circulatory, respiratory, and o those enrolled in AVMA accredited veterinary technology schools. r reproductive systems. As of 2007, international membership is also available. Dr. There are some similarities between human and equine anatomy, but there are a great many differ- A Glossary to Get You Started ences as well. For example, the human knee and the equine stifle have a lot in common. The equine We will begin this discussion of equine radius is similar to the human forearm. The equine carpal or knee bones are similar to human wrist For more information and to become a member, anatomy with Kainer’s and McCracken’s bones. And the equine splint bones compare to human fingers. please visit our web site at www.aaevt.org 4 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 5 6) Well-developed skin glands. salts through sweat glands, senses the en- entering the body. If this superficial layer very quickly when adequate cooling does Again, we turn to McCracken and Kainer 7) Large heart and lungs. vironment, and synthesizes vitamin D in of the epidermis were removed, the skin not occur. Without proper cooling, body for an explanation of what occurs: “Horses 8) A uterus with short horns and a rela- response to sunlight. would be like a mucous membrane that is temperatures during endurance rides, for shed hair mostly in the spring, beginning tively large body, and a prominent de- The skin consists of various cellular and easily permeated by water and a variety of example, can rise to 106ºF (normal tem- with the belly and sides and continuing up pression in each ovary where the egg tissue components. There are two layers, agents. perature is 99.5-101.5ºF), and the ultimate onto the back. The hair cycle includes an cells are released. the epidermis and the dermis (subcutis), The hair follicles in a horse’s skin are result can be heat stroke. actively growing stage (anagen) followed 9) A large, vascular penis and a complete with the epidermis being the outer layer. quite simple, with a single hair emerging There is more involved in the thermo- by a stage (catagen) during which the set of male accessory sex glands. The two are attached by collagenous and from each pore. The hair that emerges regulation department than just sweating. hair matrix sort of shrinks (atrophies) and There are subtle shifts in terminology as There are similarities between human elastic connective tissue. from these pores serves as frontline protec- An intricate system of blood vessels must peels away from its blood supply. A longer, we move about the equine anat omy. For and equine anatomy, but there are many The main activity of the epidermis is to tion for the horse. First, a heavier growth first carry heat from the core of the body quiescent period (telogen) then occurs in example, the two writers point out, “Distal differences too. For example, the human produce two types of protein—keratin and in cold weather helps to provide warmth to the skin so that it can be dissipated via which the hair (club hair) separates from to and including the carpus (knee), dorsal knee and the equine stifle have a lot in com- melanin. Keratin, the principal component and a lighter coat during summer facili- sweating. When heat buildup overpowers the hair matrix, but remains in the follicle. replaces cranial and palmar replaces cau- mon. The equine radius is similar to the hu- of the epidermis, is a simple protein char- tates the cooling process. The hair also the horse’s ability to dissipate it, the result The matrix later becomes active and be- dal. Distal to and including the hock, dor- man forearm. Equine carpal (knee) bones acterized by its insolubility (it won’t dis- serves as an important filtering system. can be deadly. gins to grow a new hair that pushes out sal replaces cranial, but plantar replaces compare to human wrist bones. And equine solve) and fibrous structure. It serves a sup- For example, ultraviolet light is filtered by the old club hair (shedding).” caudal.” This means that when you are splint bones compare to human fingers. portive and protective function, including the hair coat and is absorbed by melanin There are health conditions that can talking about the lower limbs, you use the There is also a similarity in the cooling the shedding of water. Melanin is the dark, granules in the epidermis and hair. Hair is overpower the forces of nature in the shed- word dorsal to mean frontward instead process during exercise—both humans and shapeless pigment of the skin and hair. composed of keratinized epithelial cells. Skin is the horse’s larg- ding department. For example, horses suf- of cranial, and instead of using caudal to horses cool their bodies via sweating. Yet, Another cell type in the epidermis is the Each hair consists of a shaft and a root fering from Cushing’s disease often carry mean rearward, you use palmar (for the the two are worlds apart when looking at Langerhans’ cell, a non-neural cell that is that is contained in a depression known as est organ, ranging from a heavy coat even during long-light, hot front limb) or plantar (for the hind limb). the digestive process. active in the immune response and possi- the hair follicle. Associated with hair fol- 12-24% of the animal’s summer days. The solar surface of the hoof is the part bly in the regulation of keratin formation. licles are sebaceous (oil) glands and bun- The color of a horse’s hair is determined that contacts the ground. Skin The most important part of the epider- dles of smooth muscle connecting the side total weight. by a rather complicated genetic process When looking at a horse’s limb from the When discussing equine anatomy, what mis is the superficial layer—known as of the hair to the dermis. The sebaceous involving the amount of pigment in the front, an axial structure is located toward better place to start than with the skin, the the stratum corneum—since much of the glands secrete an oily substance into the hair. There are three basic hair pigments— the axis (center of the limb) and an abaxial horse’s largest organ, ranging from 12-24% functional activity of the skin resides here. follicles and thus to the epidermal surface. black, brown, and yellow. The great varia- structure is located away from the axis. of the animal’s total weight depending on The proper functioning of this superficial The oil lubricates the skin to prevent ex- The problem develops something likes tion in color has to do with combinations age. It serves a number of functions. It layer is dependent on the structural ar- cessive evaporation that can result in dry this: As heat accumulates, blood flow to or absences of these three pigments. Classifying the Horse protects underlying tissues from injury, rangement of the keratin it contains and skin. the skin is increased to speed up the trans- Before leaving our Atlas authors, we’ll drying, water absorption, and bacterial on its lipids—fats and fat-like substances There are two types of sweat glands in portation of heat from the core of the body Skin Problems pass along their explanation of proper ter- invasion. Another important role involves characterized by being water-insoluble. the horse—the apocrine and the eccrine to the skin surface. As exercise increases, The skin, as the first line of defense minology for this animal we are dis cussing, thermoregulation (regulation of body tem- Lipids and keratin combine to waterproof glands. The apocrine glands are spread however, sweat loss leads to dehydration against the elements, insects, and antigens, along with what they consider to be identi- perature). The skin also excretes water and the skin and prevent various agents from throughout the skin, while the eccrine and the loss of plasma water from the is under almost constant attack from one fying characteristics: glands are found only in the frog of the bloodstream. This results in a decrease in source or another. In many cases, the con- “Horses and their close relatives, don keys hoof and, thus, play a very limited role in the volume of blood that is carrying heat ditions are not life-threatening, but produce and zebras, are in the mammalian order of Planes of the Horse the cooling process. The horse sweats the to the surface. The result is an increased a great deal of irritation to the horse and odd-toed, hoofed animals (Perissodactyla) most of any of the domestic species. The heart rate as the horse’s body desperately can lead to more serious consequences. as are their distant relatives, rhinoceroses sweat glands are simple, coiled, tubular tries to make up for the decreased volume Here are some of the attackers that make and tapirs. The horse, Equus caballus, is an Dorsal glands that open independently of the hair of blood. Very quickly, body temperature war on the skin: Cranial Caudal equid, a member of the horse family Equi- follicle. rises and extreme fatigue sets in. Dermatitis—This is an inclusive term for dae. The adjective equine is frequently used Frontal plane Nerve endings in the dermis, just under A problem that afflicts some horses and inflammation of the skin that can be pro- improperly as a noun.” the epidermis, are called sensory nerves compromises the thermoregulatory system duced by many agents, such as external ir- They point out that characteristics of and carry sensations of pressure, pain, is anhidrosis or dry coat. Horses with this ritants; burns; allergens; trauma; bacteria; equids include: Cranial heat, and cold. In contrast, motor nerves affliction simply can’t sweat. It appears that viral, parasitic or fungal infections; and sys- 1) Highly specialized limbs, each with one cause the sweat glands to secrete. anhidrosis is climate-specific; the signs are temic diseases. When dermatitis surfaces, digit (the third) and with the main mus- Rostral When sweat reaches the surface of the found in areas with a hot, humid climate, the important thing is to determine the cle mass of the limb situated close to the skin, it evaporates. This has a cooling ef- such as Florida during the summer. underlying cause, as treatment can vary body’s trunk. fect on the horse’s body. Since sweating No one is sure what causes anhidrosis, a great deal. An example of dermatitis is 2) Large paranasal sinuses within the is the horse’s primary method of cooling and there is no effective way to treat it oth- ringworm, which is actually an infection of skull. the body during exercise, cooling can be er than to move affected horses to a cooler keratinized tissue by one of several types Dorsal plane 3) Guttural pouches, which are large out- Proxi- severely compromised when evaporation climate. Often, racehorses that suffer from of fungi. The most common form of ring- pocketings of the auditory tubes that mal Axial of that sweat does not take place, such as anhidrosis in Florida will show no signs worm—which is easily transmitted from Frontal plane extend from the nasopharynx to the Abaxial on a hot, humid day. Unfortunately, nature of the affliction when moved to the cooler animals to humans—produces skin lesions Sagittal plane middle ears. didn’t provide much in the way of backup Midwest. that appear as small rounded spots in the 4) High-crowned permanent teeth that Transverse plane or meas ures for hot, humid weather, and it is The growth and shedding of hair coats skin. The lesions eventually form blisters cross-section grow for a long time—a feature used to Distal up to the humans involved to help out by follows a definite cyclical pattern. A heavi- and break, leaving scabs in their wake. Dorsal Plantar determine the age of a horse. Dorsal Palmar providing plenty of water to drink and cool er coat grows when days shorten and rain rot—This condition carries the 5) A simple stomach followed by a long Median plane mists or baths to cool the body when hors- weather turns colder, with shorter periods scientific name of dermatophilosis. It is a small intestine and a large, complicated Lateral es must be exercised in such conditions. of daylight, and is shed when days become form of dermatitis that is more common Medial large intestine where fermentation of Solar Research has shown that a horse’s body longer and warmer and there are longer in wet, humid climates than in arid areas. Ventral feed occurs. temperature can rise to a dangerous level periods of light. The condition is caused by a fungus that

6 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 7 6) Well-developed skin glands. salts through sweat glands, senses the en- entering the body. If this superficial layer very quickly when adequate cooling does Again, we turn to McCracken and Kainer 7) Large heart and lungs. vironment, and synthesizes vitamin D in of the epidermis were removed, the skin not occur. Without proper cooling, body for an explanation of what occurs: “Horses 8) A uterus with short horns and a rela- response to sunlight. would be like a mucous membrane that is temperatures during endurance rides, for shed hair mostly in the spring, beginning tively large body, and a prominent de- The skin consists of various cellular and easily permeated by water and a variety of example, can rise to 106ºF (normal tem- with the belly and sides and continuing up pression in each ovary where the egg tissue components. There are two layers, agents. perature is 99.5-101.5ºF), and the ultimate onto the back. The hair cycle includes an cells are released. the epidermis and the dermis (subcutis), The hair follicles in a horse’s skin are result can be heat stroke. actively growing stage (anagen) followed 9) A large, vascular penis and a complete with the epidermis being the outer layer. quite simple, with a single hair emerging There is more involved in the thermo- by a stage (catagen) during which the set of male accessory sex glands. The two are attached by collagenous and from each pore. The hair that emerges regulation department than just sweating. hair matrix sort of shrinks (atrophies) and There are subtle shifts in terminology as There are similarities between human elastic connective tissue. from these pores serves as frontline protec- An intricate system of blood vessels must peels away from its blood supply. A longer, we move about the equine anat omy. For and equine anatomy, but there are many The main activity of the epidermis is to tion for the horse. First, a heavier growth first carry heat from the core of the body quiescent period (telogen) then occurs in example, the two writers point out, “Distal differences too. For example, the human produce two types of protein—keratin and in cold weather helps to provide warmth to the skin so that it can be dissipated via which the hair (club hair) separates from to and including the carpus (knee), dorsal knee and the equine stifle have a lot in com- melanin. Keratin, the principal component and a lighter coat during summer facili- sweating. When heat buildup overpowers the hair matrix, but remains in the follicle. replaces cranial and palmar replaces cau- mon. The equine radius is similar to the hu- of the epidermis, is a simple protein char- tates the cooling process. The hair also the horse’s ability to dissipate it, the result The matrix later becomes active and be- dal. Distal to and including the hock, dor- man forearm. Equine carpal (knee) bones acterized by its insolubility (it won’t dis- serves as an important filtering system. can be deadly. gins to grow a new hair that pushes out sal replaces cranial, but plantar replaces compare to human wrist bones. And equine solve) and fibrous structure. It serves a sup- For example, ultraviolet light is filtered by the old club hair (shedding).” caudal.” This means that when you are splint bones compare to human fingers. portive and protective function, including the hair coat and is absorbed by melanin There are health conditions that can talking about the lower limbs, you use the There is also a similarity in the cooling the shedding of water. Melanin is the dark, granules in the epidermis and hair. Hair is overpower the forces of nature in the shed- word dorsal to mean frontward instead process during exercise—both humans and shapeless pigment of the skin and hair. composed of keratinized epithelial cells. Skin is the horse’s larg- ding department. For example, horses suf- of cranial, and instead of using caudal to horses cool their bodies via sweating. Yet, Another cell type in the epidermis is the Each hair consists of a shaft and a root fering from Cushing’s disease often carry mean rearward, you use palmar (for the the two are worlds apart when looking at Langerhans’ cell, a non-neural cell that is that is contained in a depression known as est organ, ranging from a heavy coat even during long-light, hot front limb) or plantar (for the hind limb). the digestive process. active in the immune response and possi- the hair follicle. Associated with hair fol- 12-24% of the animal’s summer days. The solar surface of the hoof is the part bly in the regulation of keratin formation. licles are sebaceous (oil) glands and bun- The color of a horse’s hair is determined that contacts the ground. Skin The most important part of the epider- dles of smooth muscle connecting the side total weight. by a rather complicated genetic process When looking at a horse’s limb from the When discussing equine anatomy, what mis is the superficial layer—known as of the hair to the dermis. The sebaceous involving the amount of pigment in the front, an axial structure is located toward better place to start than with the skin, the the stratum corneum—since much of the glands secrete an oily substance into the hair. There are three basic hair pigments— the axis (center of the limb) and an abaxial horse’s largest organ, ranging from 12-24% functional activity of the skin resides here. follicles and thus to the epidermal surface. black, brown, and yellow. The great varia- structure is located away from the axis. of the animal’s total weight depending on The proper functioning of this superficial The oil lubricates the skin to prevent ex- The problem develops something likes tion in color has to do with combinations age. It serves a number of functions. It layer is dependent on the structural ar- cessive evaporation that can result in dry this: As heat accumulates, blood flow to or absences of these three pigments. Classifying the Horse protects underlying tissues from injury, rangement of the keratin it contains and skin. the skin is increased to speed up the trans- Before leaving our Atlas authors, we’ll drying, water absorption, and bacterial on its lipids—fats and fat-like substances There are two types of sweat glands in portation of heat from the core of the body Skin Problems pass along their explanation of proper ter- invasion. Another important role involves characterized by being water-insoluble. the horse—the apocrine and the eccrine to the skin surface. As exercise increases, The skin, as the first line of defense minology for this animal we are dis cussing, thermoregulation (regulation of body tem- Lipids and keratin combine to waterproof glands. The apocrine glands are spread however, sweat loss leads to dehydration against the elements, insects, and antigens, along with what they consider to be identi- perature). The skin also excretes water and the skin and prevent various agents from throughout the skin, while the eccrine and the loss of plasma water from the is under almost constant attack from one fying characteristics: glands are found only in the frog of the bloodstream. This results in a decrease in source or another. In many cases, the con- “Horses and their close relatives, don keys hoof and, thus, play a very limited role in the volume of blood that is carrying heat ditions are not life-threatening, but produce and zebras, are in the mammalian order of Planes of the Horse the cooling process. The horse sweats the to the surface. The result is an increased a great deal of irritation to the horse and odd-toed, hoofed animals (Perissodactyla) most of any of the domestic species. The heart rate as the horse’s body desperately can lead to more serious consequences. as are their distant relatives, rhinoceroses sweat glands are simple, coiled, tubular tries to make up for the decreased volume Here are some of the attackers that make and tapirs. The horse, Equus caballus, is an Dorsal glands that open independently of the hair of blood. Very quickly, body temperature war on the skin: Cranial Caudal equid, a member of the horse family Equi- follicle. rises and extreme fatigue sets in. Dermatitis—This is an inclusive term for dae. The adjective equine is frequently used Frontal plane Nerve endings in the dermis, just under A problem that afflicts some horses and inflammation of the skin that can be pro- improperly as a noun.” the epidermis, are called sensory nerves compromises the thermoregulatory system duced by many agents, such as external ir- They point out that characteristics of and carry sensations of pressure, pain, is anhidrosis or dry coat. Horses with this ritants; burns; allergens; trauma; bacteria; equids include: Cranial heat, and cold. In contrast, motor nerves affliction simply can’t sweat. It appears that viral, parasitic or fungal infections; and sys- 1) Highly specialized limbs, each with one cause the sweat glands to secrete. anhidrosis is climate-specific; the signs are temic diseases. When dermatitis surfaces, digit (the third) and with the main mus- Rostral When sweat reaches the surface of the found in areas with a hot, humid climate, the important thing is to determine the cle mass of the limb situated close to the skin, it evaporates. This has a cooling ef- such as Florida during the summer. underlying cause, as treatment can vary body’s trunk. fect on the horse’s body. Since sweating No one is sure what causes anhidrosis, a great deal. An example of dermatitis is 2) Large paranasal sinuses within the is the horse’s primary method of cooling and there is no effective way to treat it oth- ringworm, which is actually an infection of skull. the body during exercise, cooling can be er than to move affected horses to a cooler keratinized tissue by one of several types Dorsal plane 3) Guttural pouches, which are large out- Proxi- severely compromised when evaporation climate. Often, racehorses that suffer from of fungi. The most common form of ring- pocketings of the auditory tubes that mal Axial of that sweat does not take place, such as anhidrosis in Florida will show no signs worm—which is easily transmitted from Frontal plane extend from the nasopharynx to the Abaxial on a hot, humid day. Unfortunately, nature of the affliction when moved to the cooler animals to humans—produces skin lesions Sagittal plane middle ears. didn’t provide much in the way of backup Midwest. that appear as small rounded spots in the 4) High-crowned permanent teeth that Transverse plane or meas ures for hot, humid weather, and it is The growth and shedding of hair coats skin. The lesions eventually form blisters cross-section grow for a long time—a feature used to Distal up to the humans involved to help out by follows a definite cyclical pattern. A heavi- and break, leaving scabs in their wake. Dorsal Plantar determine the age of a horse. Dorsal Palmar providing plenty of water to drink and cool er coat grows when days shorten and rain rot—This condition carries the 5) A simple stomach followed by a long Median plane mists or baths to cool the body when hors- weather turns colder, with shorter periods scientific name of dermatophilosis. It is a small intestine and a large, complicated Lateral es must be exercised in such conditions. of daylight, and is shed when days become form of dermatitis that is more common Medial large intestine where fermentation of Solar Research has shown that a horse’s body longer and warmer and there are longer in wet, humid climates than in arid areas. Ventral feed occurs. temperature can rise to a dangerous level periods of light. The condition is caused by a fungus that

6 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 7 the result is tearing of the skin, which often means that the horse can see objects with coffin bone. The structure of these bones The primary sex organs of the stallion cells, and platelets. The red blood cells have results in a death sen tence for the horse. one eye. As a result, the brain often gets and their functional relationship to each are the two testicles, which produce semen a protein known as hemoglobin that binds There is no known treatment. two images simultaneously. With binocular other helps determines a horse’s athletic and testosterone, and the penis. oxygen and conveys it to the muscles. The vision the horse can focus with both eyes potential and its capability of remaining A horse’s respiratory system is de signed— white blood cells function in the immune Stay Tuned… and the brain is receiving only one signal. sound even under an exacting exercise and as is the case with other mam mals—to system by defending against foreign invad- There, in short form, is a description Humans have binocular vision only. performance regimen. exchange oxygen and carbon dioxide. Air ers, such as harmful bacteria, and the plate- of the equine skin and its functions. In up- From the equine head, we move to the The angles at which the bones connect enters the nostrils, passes through the long lets are involved with blood clotting. H coming articles, we will concentrate on dif- neck. There are seven cervical vertebrae in have much to do with the horse’s physical nasal cavity over the pharynx and larynx, About the Author is capable of creating infection when con- ferent parts of the horse’s anatomy with an the horse’s neck, with the spinal cord run- capability and its continued well being. then enters the trachea that carries it to the Les Sellnow is a free-lance writer based near Riverton, ditions are right, such as during hot and in-depth look at how they are structured, ning through them. The neck blends into The leg bones, as well as other bones, are lungs. Wyo. He specializes in articles on equine research, and he humid periods. The infection results in the functions they serve, and what is in- the back at the withers. connected at joints. There are three types A horse’s cardiovascular system consists operates a ranch where he raises horses and livestock. He scabby spots that are devoid of hair when volved in keeping them healthy. We come now to the horse’s rib struc- of equine joints—synovial, which are mov- of blood, a series of blood vessels through has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the rubbed free. Here is a brief look at those upcoming ture. Normally, there are 18 pairs of ribs able; cartilaginous, which are slightly mov- which blood flows, and a heart that pumps young Horse, and the Journey of the western Horse, pub- Mange—This condition is caused by sev- article topics, to whet your appetite. in the horse, but a nineteenth rib on one able; and fibrous, which are immovable. blood throughout the horse’s body. Blood is lished by Eclipse Press and available at www.Exclusively Equine.com or by calling 800/582-5604. eral species of mites. Mange is character- The equine skull houses the brain and side or both is not considered all that rare. The joints that connect the horses’ front comprised of red blood cells, white blood ized by loss of hair, itching, and intense the most important organs of sense. There Eight pairs of ribs are known as true ribs. leg bones are synovial. A synov ial joint con- irritation to the skin. are 34 bones in the equine skull, most of They join the segments of the sternum or sists of two bone ends, covered by articular Lice—Horses can har- breastbone. The oth- cartilage. The cartilage within the joint is bor two species of lice. er 10 are known as smooth and resilient, allowing for friction- One species, Damalinia floating ribs—merely less movement. Ligaments keep the bones equi, is the horse bit- Horses, donkeys, and zebras are in the mammalian overlapping and be- in proper support and relationship. Required Reading ing louse and the other, order of odd-toed, hoofed animals (Perissodactyla) ing at tached to each In the rear legs, we’ll start at the spine Haema topinus asini, is other. The seventh where the ilium, the largest of three bones for Responsible Horse Owners. the horse sucking louse. as are their distant relatives, rhinoceroses and and eighth ribs are in the pelvis, connects with the spinal col- Afflicted horses will the longest. Those umn. The ilium angles down and rearward show signs of itching by tapirs. toward the rear are to blend into the femur or thigh bone. The constantly rubbing and much shorter. femur angles slightly forward to the stifle. For over 10 years The Horse: Your Guide to Equine biting at affected areas. Next we switch to Beginning at the stifle (comparable to the Health Care has been essential reading by responsible Lice are most often found in un thrifty them flat. During the birthing process, the horse’s thoracic or front limbs. Each knee in humans) is the tibia, which contin- horse owners. horses and quickly add to the poor condi- these bones yield and overlap, allowing the of these consists of the scapula, humerus, ues downward to the hock. From the hock tion status. In severe infestations, the horse skull to be somewhat compressed and thus radius, ulna, seven or eight car pal bones, to the pastern is the metatarsus or rear Subscribe today, and along with your full access to might lose patches of hair. allowing for easier parturition. cannon bone, two splint bones, two proxi- cannon bone, which connects with the TheHorse.com, you’ll receive 12 issues of The Horse Dandruff—This is a condition where The horse has unique eyes—they are mal sesamoid bones, large pastern bone, long pastern bone; next is the short pas- filled with essential information you need to know to the horse’s skin becomes scaly and the both monocular and binocular. Monocular small pastern bone, navicular bone, and tern bone, and lastly the coffin bone. Both keep your horses healthy and strong. Order now and hair coat often is dry and dirty. In some front and rear limbs are con nected and sup- instances, the hair will fall out. Grooming ported by ligaments, tendons, and muscles SAVE OVER 72% off the cover price. Plus, you’ll get the can help to stimulate the sebaceous glands; Anatomy of the Skin that provide attachment and mobility. next edition of The Horse Source FREE. exercise and a proper diet can prevent this Melanocyte Nature didn’t do the horse many favors Sweat pore NO RISK. NO OBLIGATION. problem and can work to solve it if it does Keratin Cells when designing the way in which it pro- occur. cesses food. Its stomach can hold only Your satisfaction is absolutely guaranteed. If you’re Biting Insects—During the summer small amounts of food—eight to 16 quarts not completely satisfied, we’ll send you a refund for all months, horses are under almost constant at a time. The stomach empties into the Stratum cor- unmailed issues! attack by one type of biting insect or an- } neum small intestine, a tube that connects with other, including flies, mosquitoes, and Epidermis the large intestine. The small intestine is ticks. Not only are these pests irritating } approximately 70 feet long, with a capacity to the horse, but they also spread diseases of about 12 gallons. The large intestine of such as West Nile virus, equine infectious the horse is divided into four parts—the ce- anemia, and encephalitis. Responsible ustration cum, which is about four feet long and one LL SUBSCRIBE NOW! horse owners should take all steps that are Dermis foot wide; the great colon, which is about possible to prevent these disease-carrying 12 feet long and 10 inches wide; the small CLICK HERE or Shaft pests from attacking the animals in their colon, which is about 10 feet long and four charge. inches wide; and the rectum. call 1-800-582-5604 Root hyperelastosis cutis (hC)—This is an in- Sebaceous in Peterson i In the reproductive department, the B

gland o main sex organs of the mare are two ova- herited condition of Quarter Horses from a } r Subcutis particular bloodline. Earlier, we mentioned ries that produce eggs, which are housed } Dr. that the epidermis and dermis are held to- in follicles. When an egg is mature, it Nerve Sweat gland gether by collagenous material, sort of like Hair follicle Smooth muscle leaves the follicle and travels through the glue that can bind two substances. When The skin protects underlying tissues from injury, drying, water absorption, and bacterial invasion. infundibulum and oviduct to the uterus. If a horse inherits the genes that cause HC, Another important role involves thermoregulation (regulation of body temperature); the skin also fertilized, it grows within the uterus from excretes water and salts through sweat glands, senses the environment, and synthesizes vitamin D CQ06Z236TH the collagenous material is defective and a minute structure into a foal that is born in response to sunlight. unable to hold the two skin layers together; through the vagina.

8 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 9 the result is tearing of the skin, which often means that the horse can see objects with coffin bone. The structure of these bones The primary sex organs of the stallion cells, and platelets. The red blood cells have results in a death sen tence for the horse. one eye. As a result, the brain often gets and their functional relationship to each are the two testicles, which produce semen a protein known as hemoglobin that binds There is no known treatment. two images simultaneously. With binocular other helps determines a horse’s athletic and testosterone, and the penis. oxygen and conveys it to the muscles. The vision the horse can focus with both eyes potential and its capability of remaining A horse’s respiratory system is de signed— white blood cells function in the immune Stay Tuned… and the brain is receiving only one signal. sound even under an exacting exercise and as is the case with other mam mals—to system by defending against foreign invad- There, in short form, is a description Humans have binocular vision only. performance regimen. exchange oxygen and carbon dioxide. Air ers, such as harmful bacteria, and the plate- of the equine skin and its functions. In up- From the equine head, we move to the The angles at which the bones connect enters the nostrils, passes through the long lets are involved with blood clotting. H coming articles, we will concentrate on dif- neck. There are seven cervical vertebrae in have much to do with the horse’s physical nasal cavity over the pharynx and larynx, About the Author is capable of creating infection when con- ferent parts of the horse’s anatomy with an the horse’s neck, with the spinal cord run- capability and its continued well being. then enters the trachea that carries it to the Les Sellnow is a free-lance writer based near Riverton, ditions are right, such as during hot and in-depth look at how they are structured, ning through them. The neck blends into The leg bones, as well as other bones, are lungs. Wyo. He specializes in articles on equine research, and he humid periods. The infection results in the functions they serve, and what is in- the back at the withers. connected at joints. There are three types A horse’s cardiovascular system consists operates a ranch where he raises horses and livestock. He scabby spots that are devoid of hair when volved in keeping them healthy. We come now to the horse’s rib struc- of equine joints—synovial, which are mov- of blood, a series of blood vessels through has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the rubbed free. Here is a brief look at those upcoming ture. Normally, there are 18 pairs of ribs able; cartilaginous, which are slightly mov- which blood flows, and a heart that pumps young Horse, and the Journey of the western Horse, pub- Mange—This condition is caused by sev- article topics, to whet your appetite. in the horse, but a nineteenth rib on one able; and fibrous, which are immovable. blood throughout the horse’s body. Blood is lished by Eclipse Press and available at www.Exclusively Equine.com or by calling 800/582-5604. eral species of mites. Mange is character- The equine skull houses the brain and side or both is not considered all that rare. The joints that connect the horses’ front comprised of red blood cells, white blood ized by loss of hair, itching, and intense the most important organs of sense. There Eight pairs of ribs are known as true ribs. leg bones are synovial. A synov ial joint con- irritation to the skin. are 34 bones in the equine skull, most of They join the segments of the sternum or sists of two bone ends, covered by articular Lice—Horses can har- breastbone. The oth- cartilage. The cartilage within the joint is bor two species of lice. er 10 are known as smooth and resilient, allowing for friction- One species, Damalinia floating ribs—merely less movement. Ligaments keep the bones equi, is the horse bit- Horses, donkeys, and zebras are in the mammalian overlapping and be- in proper support and relationship. Required Reading ing louse and the other, order of odd-toed, hoofed animals (Perissodactyla) ing at tached to each In the rear legs, we’ll start at the spine Haema topinus asini, is other. The seventh where the ilium, the largest of three bones for Responsible Horse Owners. the horse sucking louse. as are their distant relatives, rhinoceroses and and eighth ribs are in the pelvis, connects with the spinal col- Afflicted horses will the longest. Those umn. The ilium angles down and rearward show signs of itching by tapirs. toward the rear are to blend into the femur or thigh bone. The constantly rubbing and much shorter. femur angles slightly forward to the stifle. For over 10 years The Horse: Your Guide to Equine biting at affected areas. Next we switch to Beginning at the stifle (comparable to the Health Care has been essential reading by responsible Lice are most often found in un thrifty them flat. During the birthing process, the horse’s thoracic or front limbs. Each knee in humans) is the tibia, which contin- horse owners. horses and quickly add to the poor condi- these bones yield and overlap, allowing the of these consists of the scapula, humerus, ues downward to the hock. From the hock tion status. In severe infestations, the horse skull to be somewhat compressed and thus radius, ulna, seven or eight car pal bones, to the pastern is the metatarsus or rear Subscribe today, and along with your full access to might lose patches of hair. allowing for easier parturition. cannon bone, two splint bones, two proxi- cannon bone, which connects with the TheHorse.com, you’ll receive 12 issues of The Horse Dandruff—This is a condition where The horse has unique eyes—they are mal sesamoid bones, large pastern bone, long pastern bone; next is the short pas- filled with essential information you need to know to the horse’s skin becomes scaly and the both monocular and binocular. Monocular small pastern bone, navicular bone, and tern bone, and lastly the coffin bone. Both keep your horses healthy and strong. Order now and hair coat often is dry and dirty. In some front and rear limbs are con nected and sup- instances, the hair will fall out. Grooming ported by ligaments, tendons, and muscles SAVE OVER 72% off the cover price. Plus, you’ll get the can help to stimulate the sebaceous glands; Anatomy of the Skin that provide attachment and mobility. next edition of The Horse Source FREE. exercise and a proper diet can prevent this Melanocyte Nature didn’t do the horse many favors Sweat pore NO RISK. NO OBLIGATION. problem and can work to solve it if it does Keratin Cells when designing the way in which it pro- occur. cesses food. Its stomach can hold only Your satisfaction is absolutely guaranteed. If you’re Biting Insects—During the summer small amounts of food—eight to 16 quarts not completely satisfied, we’ll send you a refund for all months, horses are under almost constant at a time. The stomach empties into the Stratum cor- unmailed issues! attack by one type of biting insect or an- } neum small intestine, a tube that connects with other, including flies, mosquitoes, and Epidermis the large intestine. The small intestine is ticks. Not only are these pests irritating } approximately 70 feet long, with a capacity to the horse, but they also spread diseases of about 12 gallons. The large intestine of such as West Nile virus, equine infectious the horse is divided into four parts—the ce- anemia, and encephalitis. Responsible ustration cum, which is about four feet long and one LL SUBSCRIBE NOW! horse owners should take all steps that are Dermis foot wide; the great colon, which is about possible to prevent these disease-carrying 12 feet long and 10 inches wide; the small CLICK HERE or Shaft pests from attacking the animals in their colon, which is about 10 feet long and four charge. inches wide; and the rectum. call 1-800-582-5604 Root hyperelastosis cutis (hC)—This is an in- Sebaceous in Peterson i In the reproductive department, the B gland o main sex organs of the mare are two ova- herited condition of Quarter Horses from a } r Subcutis particular bloodline. Earlier, we mentioned ries that produce eggs, which are housed } Dr. that the epidermis and dermis are held to- in follicles. When an egg is mature, it Nerve Sweat gland gether by collagenous material, sort of like Hair follicle Smooth muscle leaves the follicle and travels through the glue that can bind two substances. When The skin protects underlying tissues from injury, drying, water absorption, and bacterial invasion. infundibulum and oviduct to the uterus. If a horse inherits the genes that cause HC, Another important role involves thermoregulation (regulation of body temperature); the skin also fertilized, it grows within the uterus from excretes water and salts through sweat glands, senses the environment, and synthesizes vitamin D CQ06Z236TH the collagenous material is defective and a minute structure into a foal that is born in response to sunlight. unable to hold the two skin layers together; through the vagina.

8 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 9 By Les seLLnow

here are 205 bones in the horse’s skeleton. Twenty of these bones are in each foreleg and 20 in each hind limb, for a grand total of 80 bones in the four equine legs. TThe leg bones do not function independently. Each is connected or aligned with one or more other bones, allowing the horse to lift, bend, and flex its legs. This ability allows the horse to travel across the ground, absorbing concussion as it does so. The spot where one or more bones join is the joint. This installment of the anatomy and physiology series focuses on these critical areas of movement.

Types of Joints There are three types or classifications of equine joints. They are: synovial joints—These are the movable joints and the ones most apt to sustain injury or be afflicted with disease. An example of a synovial joint is the carpus (knee), which actually contains three joints and mul tiple bones. In a manner of speaking, the synovial joints are the horse’s ball bearings. A synovial joint consists of two bone ends that are both covered by articular cartilage. The cartilage within the joint is smooth and resilient, allowing for frictionless movement. Each joint capsule also contains an inner lining called the synovial membrane, which secretes synovial fluid to lubricate the joints.

Proper movement of the horse is dependent on proper functioning of his joints

Cartilaginous joints—These joints are slightly movable or immovable, depending on the bones involved. Cartilaginous joints are united by fi- brocartilage (composed of collagen fibers), hyaline cartilage (translucent bluish white), or both. An example is the connective tissue between vertebrae. Fibrous joints—These are immovable joints where the bones are bound by fibrous tissue that ossifies (hardens into bone) as the horse matures. An example would be joints within the equine skull. We’ll concentrate on synovial joints because they are the most active and are more prone to problems than joints with little or no movement. As in the opening article of this series in Jan uary, we will point out that information for this article is drawn from many textbooks and scientific papers that have been

editor’s Note This is the second in a 12-part series of articles on equine anatomy and physiology. Future topics include the foreleg, the hind limb, the hoof, the head and neck, the back, muscles, tendons and ligaments, the digestive system, the circulatory and respiratory systems, and the reproductive system. Dr. roBin Peterson iLLustrations

10 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 11 By Les seLLnow

Proper movement of the horse is dependent on proper functioning of his joints

10 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 11 within the fibrous capsule are covered prop erly—for movement and as a concus- nature, but there are exceptions. A key ex- l eft Stifle Joint: by a strong web of ligaments, muscles, and with cartilage, which primarily is hyaline sion absorber—is compromised. ception is the knee, which almost seems to n ormal and with o C d tendons. The elbow joint also works like a cartilage—a substance that is flexible and There is a second method for lubricating have been con structed haphazardly. There hinge, with movement on only one plane, somewhat elastic. Beneath the cartilage in cartilage in a joint. Fluid is stored within are eight bones in the horse’s knee and and it is stabilized by medial and lateral femur each bone end is subchondral bone. the cartilage and when weight bear ing oc- three main joints to keep them all aligned ligaments. We mentioned earlier that the synovial curs, it is squeezed out of the cartilage onto and functioning properly, which is no membrane secretes lubricating fluid that the surface. When weight bearing ceases, small task. The eight bones are arranged The Hind Limb patella lateral allows a healthy joint to have frictionless the fluid is reabsorbed by the cartilage. in two rows. trochlear The rear fetlock, pastern, and coffin movement. In addition to being a lubri- The three prime knee joints are located ridge joints correspond to their front leg coun- published. However, we would be re- cant, synovial fluid also supplies nutrients The Front Limb thusly: One between the radius and prox- of femur terparts, although they usually have steeper miss in not calling attention to the three and removes waste from hyaline articular Injury and disease to the front limb imal (upper) row of four carpal bones; one angulations because the back limbs are medial key sources for the information that fol- cartilage. Synovial fluid is described as joints are more common than injury to the between the two rows of carpal bones (usu- trochlear used more for propulsion than shock lows. One is Anatomy of Domestic Animals, having the consistency of raw egg white. rear limbs. Why? A horse carries 60-65% ally there are four bones per row), and one ridge absorption. a textbook authored by Chris Pasquini, An important component in the makeup of its weight on the front end. This means between the distal (lower) row of carpal of femur Two additional joints in the rear DVM, MS, and Tom Spurgeon, PhD, of the of synovial fluid is hyaluronic acid, also that the joints of the front limbs are sub- bones and the cannon and splint bones. end deserve discussion because Department of Anatomy and Neurobiol- known as sodium hyaluronate or hyalu ron- jected to a greater share of the concussion There also are tiny joints between the in- they are highly important in the ogy at Colorado State University. an. It is primarily responsible for giving with each step the horse takes than are the dividual carpal bones. horse’s ability to perform prop- Two other key sources are C. Wayne Mc- the synovial fluid its lubricating capability. rear limbs, especially during strenuous ac- Because the knee is structured with mul- erly. They are the hock joint and Ilwraith, BVSc, PhD, MS, MRCVS, Direc- When disease strikes a joint, there often tivities such as racing and jumping. tiple bones, it becomes immediately appar- the stifle joint. The hock joint is tor of Orthopaedic Re search at the College is a depletion of hyaluronic acid. When For the most part, construction of ent that good conformation is a prime a bit like the knee in that it is com- of Veterinary Medicine and Biomedical that happens, the joint’s ability to function equine synovial joints is a wonder of requisite in keeping this joint healthy and fibula prised of multiple bones—six, to be Sciences at Colorado State University, and strong. Any deviation, such as being over spe cif ic. However, these bones don’t have tibia Jerry Black, DVM, a California veterinar- or under at the knee, puts undue stress lateral trochlear the range of movement of the knee bones. fore (left) and hind limb anatomy Lateral Trochlear ian. Both are past presidents of the Ameri- on the complicated knee joint and opens ridgeRidge of of femur Femur Like the knee joint, strong ligaments sta- can Association of Equine Practitioners the door for a multitude of potential prob- withwith OCD OCD bilize the hock joint and facilitate move- (AAEP) and both have lectured on the sub- lems. ment. Osteochondrosis might lead to OCD or subchon- ject of joints and joint problems in horses. From the knee on down, the joint struc- The stifle joint has to be considered one scapula dral cystic lesions. OCD normally shows up in one Information for this treatise has been tak- ture is slightly less complicated. The can- joint rather than multiple joints. However, bilat- of the key joints in the equine body. It is ilium en from interviews and from presentations non bone continues downward from the eral involvement (of both front or hind limbs) similar to the human knee, and when it they have made at AAEP conventions and, knee until it joins the long pastern bone, is sufficiently common that the opposite joints becomes injured or diseased, the horse’s should always be radiographed. in Black’s case, Horseman’s Day, an owner or first phalanx (P1), at the fetlock joint. ability to move can be severely compro- education event sponsored by AAEP. Also located at this junction are the me- mised. First we’ll look at how synovial joints are hip joint dial and lateral proximal sesamoid bones. We are now down into the foot where The stifle is the largest single joint in the shoulder joint constructed, then we’ll outline where they ischiatic tuber- These bones are deeply imbedded in, and joints also play connecting and shock ab- horse. One of its functions is to cause the are located, the functions they serve, and femur osity are supported by, the suspensory ligament. sorbing roles. The coffin joint is next in rear limb to become rigid when the foot some of the problems that can develop. humerus patella They are subject to injury and fracture, line as we travel downward, and it con- is on the ground. This is controlled via particularly if the horse interferes and nects P2 with P3 (the coffin bone). This is con traction of muscles above the patella, How It Works stifle strikes them with the opposing limb. a movable joint that plays a very important which releases the stay apparatus, and is The joint structure is designed to ab sorb elbow joint joint It is amazing that more racehorses and role in absorbing concussion. the equivalent of a human’s kneecap. concussion and permit leg movement. The jumpers don’t break down at the fetlock Helping in the weight-transferring and Once again, we must call attention to the two bone ends are encased in a fibrous joint. To understand that statement, we shock absorbing roles at this location is the role of good conformation in keep ing these capsule that helps provide sta bil ity. Col- must realize that when a racehorse runs navicular bone, which is supported by the key joints healthy. Deviations—such as be- lateral ligaments, comprised of very tough at top speed, there is one point in every deep digital flexor tendon. The deep flexor ing too narrow or too wide at the hocks— tibia fibers, attach to the sides of each of the stride where its entire weight descends tendon is closely fitted to the surface of the can result in undue stress, which can lead tuber bones within the capsule, and this plays radius upon one front leg, with most of the con- navicular bone with a navicular bursa, a to a variety of hock joint problems. calcanei a major stabilizing role. Other ligaments, accessory car- cussion be ing absorbed and dissipated by fluid-filled sac that provides a smooth, lu- A clear example of a ball and joint such as the cruciate ligaments, also help pal bone hock the fetlock joint. The force of that concus- bricating substance that reduces friction. socket is the hip joint. The head, or up- stabilize some joints, including the stifle. knee joint or joint sion often drastically changes the angle of Again, we can’t get away from the im- per end, of the femur fits into the socket Other ligaments outside the joint cavity carpus carpal or knee tarsal or hock the fetlock. At rest, the fetlock generally portance of good conformation when formed by the hip. The hip joint is stabi- also lend support. A prime example would bones bones is at an angle of about 50º. When all of considering the health and maintenance lized by a strong band of ligaments. One be the distal sesamoidean ligaments and the weight comes to bear on that one leg of these joints. When any of these joints of the ligaments stabilizing the hip joint sus pensory ligaments that, to gether with splint bone when a horse runs at speed, the fetlock is are out of alignment, there is a great deal is the accessory ligament, which does not the sesamoid bones, make up the apparat- often almost level with the ground, or at more stress on them, especially when the occur in any domestic animal other than us that holds the fetlock in proper posi- cannon bone zero degrees, placing tremendous stress horse is exercising vigorously. the horse. tion. fetlock joint on the fetlock joint. There are two other joints—shoulder The outer part of the joint capsule is the proximal or first phalanx The next joint below the fetlock is the joint and elbow joint—in the forelimbs, Common Problems fibrous layer and the inner part is synovial pastern joint pastern joint. This is where P1 connects but they don’t absorb much concussion be- All of the synovial joints are subject to membrane that lines the sides of the joint middle or second phalanx with the short pastern bone, or second pha- cause the concussion already has been ab- injury or disease as the result of poor con- capsule. The joint is lubricated by synovial coffin joint lanx (P2). This joint moves very little and sorbed and dissipated by the other joints formation or the on go ing wear and tear of fluid, which is secreted by the synovial distal or third phalanx, a.k.a. coffin bone does not absorb a great deal of concussion as the first line of defense. The shoulder heavy performance demands placed on the membrane. The ends of each of the bones when compared to the fetlock joint. joint is a hinge joint that is held in place animal by its rider.

12 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 13 within the fibrous capsule are covered prop erly—for movement and as a concus- nature, but there are exceptions. A key ex- l eft Stifle Joint: by a strong web of ligaments, muscles, and with cartilage, which primarily is hyaline sion absorber—is compromised. ception is the knee, which almost seems to n ormal and with o C d tendons. The elbow joint also works like a cartilage—a substance that is flexible and There is a second method for lubricating have been con structed haphazardly. There hinge, with movement on only one plane, somewhat elastic. Beneath the cartilage in cartilage in a joint. Fluid is stored within are eight bones in the horse’s knee and and it is stabilized by medial and lateral femur each bone end is subchondral bone. the cartilage and when weight bear ing oc- three main joints to keep them all aligned ligaments. We mentioned earlier that the synovial curs, it is squeezed out of the cartilage onto and functioning properly, which is no membrane secretes lubricating fluid that the surface. When weight bearing ceases, small task. The eight bones are arranged The Hind Limb patella lateral allows a healthy joint to have frictionless the fluid is reabsorbed by the cartilage. in two rows. trochlear The rear fetlock, pastern, and coffin movement. In addition to being a lubri- The three prime knee joints are located ridge joints correspond to their front leg coun- published. However, we would be re- cant, synovial fluid also supplies nutrients The Front Limb thusly: One between the radius and prox- of femur terparts, although they usually have steeper miss in not calling attention to the three and removes waste from hyaline articular Injury and disease to the front limb imal (upper) row of four carpal bones; one angulations because the back limbs are medial key sources for the information that fol- cartilage. Synovial fluid is described as joints are more common than injury to the between the two rows of carpal bones (usu- trochlear used more for propulsion than shock lows. One is Anatomy of Domestic Animals, having the consistency of raw egg white. rear limbs. Why? A horse carries 60-65% ally there are four bones per row), and one ridge absorption. a textbook authored by Chris Pasquini, An important component in the makeup of its weight on the front end. This means between the distal (lower) row of carpal of femur Two additional joints in the rear DVM, MS, and Tom Spurgeon, PhD, of the of synovial fluid is hyaluronic acid, also that the joints of the front limbs are sub- bones and the cannon and splint bones. end deserve discussion because Department of Anatomy and Neurobiol- known as sodium hyaluronate or hyalu ron- jected to a greater share of the concussion There also are tiny joints between the in- they are highly important in the ogy at Colorado State University. an. It is primarily responsible for giving with each step the horse takes than are the dividual carpal bones. horse’s ability to perform prop- Two other key sources are C. Wayne Mc- the synovial fluid its lubricating capability. rear limbs, especially during strenuous ac- Because the knee is structured with mul- erly. They are the hock joint and Ilwraith, BVSc, PhD, MS, MRCVS, Direc- When disease strikes a joint, there often tivities such as racing and jumping. tiple bones, it becomes immediately appar- the stifle joint. The hock joint is tor of Orthopaedic Re search at the College is a depletion of hyaluronic acid. When For the most part, construction of ent that good conformation is a prime a bit like the knee in that it is com- of Veterinary Medicine and Biomedical that happens, the joint’s ability to function equine synovial joints is a wonder of requisite in keeping this joint healthy and fibula prised of multiple bones—six, to be Sciences at Colorado State University, and strong. Any deviation, such as being over spe cif ic. However, these bones don’t have tibia Jerry Black, DVM, a California veterinar- or under at the knee, puts undue stress lateral trochlear the range of movement of the knee bones. fore (left) and hind limb anatomy Lateral Trochlear ian. Both are past presidents of the Ameri- on the complicated knee joint and opens ridgeRidge of of femur Femur Like the knee joint, strong ligaments sta- can Association of Equine Practitioners the door for a multitude of potential prob- withwith OCD OCD bilize the hock joint and facilitate move- (AAEP) and both have lectured on the sub- lems. ment. Osteochondrosis might lead to OCD or subchon- ject of joints and joint problems in horses. From the knee on down, the joint struc- The stifle joint has to be considered one scapula dral cystic lesions. OCD normally shows up in one Information for this treatise has been tak- ture is slightly less complicated. The can- joint rather than multiple joints. However, bilat- of the key joints in the equine body. It is ilium en from interviews and from presentations non bone continues downward from the eral involvement (of both front or hind limbs) similar to the human knee, and when it they have made at AAEP conventions and, knee until it joins the long pastern bone, is sufficiently common that the opposite joints becomes injured or diseased, the horse’s should always be radiographed. in Black’s case, Horseman’s Day, an owner or first phalanx (P1), at the fetlock joint. ability to move can be severely compro- education event sponsored by AAEP. Also located at this junction are the me- mised. First we’ll look at how synovial joints are hip joint dial and lateral proximal sesamoid bones. We are now down into the foot where The stifle is the largest single joint in the shoulder joint constructed, then we’ll outline where they ischiatic tuber- These bones are deeply imbedded in, and joints also play connecting and shock ab- horse. One of its functions is to cause the are located, the functions they serve, and femur osity are supported by, the suspensory ligament. sorbing roles. The coffin joint is next in rear limb to become rigid when the foot some of the problems that can develop. humerus patella They are subject to injury and fracture, line as we travel downward, and it con- is on the ground. This is controlled via particularly if the horse interferes and nects P2 with P3 (the coffin bone). This is con traction of muscles above the patella, How It Works stifle strikes them with the opposing limb. a movable joint that plays a very important which releases the stay apparatus, and is The joint structure is designed to ab sorb elbow joint joint It is amazing that more racehorses and role in absorbing concussion. the equivalent of a human’s kneecap. concussion and permit leg movement. The jumpers don’t break down at the fetlock Helping in the weight-transferring and Once again, we must call attention to the two bone ends are encased in a fibrous joint. To understand that statement, we shock absorbing roles at this location is the role of good conformation in keep ing these capsule that helps provide sta bil ity. Col- must realize that when a racehorse runs navicular bone, which is supported by the key joints healthy. Deviations—such as be- lateral ligaments, comprised of very tough at top speed, there is one point in every deep digital flexor tendon. The deep flexor ing too narrow or too wide at the hocks— tibia fibers, attach to the sides of each of the stride where its entire weight descends tendon is closely fitted to the surface of the can result in undue stress, which can lead tuber bones within the capsule, and this plays radius upon one front leg, with most of the con- navicular bone with a navicular bursa, a to a variety of hock joint problems. calcanei a major stabilizing role. Other ligaments, accessory car- cussion be ing absorbed and dissipated by fluid-filled sac that provides a smooth, lu- A clear example of a ball and joint such as the cruciate ligaments, also help pal bone hock the fetlock joint. The force of that concus- bricating substance that reduces friction. socket is the hip joint. The head, or up- stabilize some joints, including the stifle. knee joint or joint sion often drastically changes the angle of Again, we can’t get away from the im- per end, of the femur fits into the socket Other ligaments outside the joint cavity carpus carpal or knee tarsal or hock the fetlock. At rest, the fetlock generally portance of good conformation when formed by the hip. The hip joint is stabi- also lend support. A prime example would bones bones is at an angle of about 50º. When all of considering the health and maintenance lized by a strong band of ligaments. One be the distal sesamoidean ligaments and the weight comes to bear on that one leg of these joints. When any of these joints of the ligaments stabilizing the hip joint sus pensory ligaments that, to gether with splint bone when a horse runs at speed, the fetlock is are out of alignment, there is a great deal is the accessory ligament, which does not the sesamoid bones, make up the apparat- often almost level with the ground, or at more stress on them, especially when the occur in any domestic animal other than us that holds the fetlock in proper posi- cannon bone zero degrees, placing tremendous stress horse is exercising vigorously. the horse. tion. fetlock joint on the fetlock joint. There are two other joints—shoulder The outer part of the joint capsule is the proximal or first phalanx The next joint below the fetlock is the joint and elbow joint—in the forelimbs, Common Problems fibrous layer and the inner part is synovial pastern joint pastern joint. This is where P1 connects but they don’t absorb much concussion be- All of the synovial joints are subject to membrane that lines the sides of the joint middle or second phalanx with the short pastern bone, or second pha- cause the concussion already has been ab- injury or disease as the result of poor con- capsule. The joint is lubricated by synovial coffin joint lanx (P2). This joint moves very little and sorbed and dissipated by the other joints formation or the on go ing wear and tear of fluid, which is secreted by the synovial distal or third phalanx, a.k.a. coffin bone does not absorb a great deal of concussion as the first line of defense. The shoulder heavy performance demands placed on the membrane. The ends of each of the bones when compared to the fetlock joint. joint is a hinge joint that is held in place animal by its rider.

12 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 13 Capsulitis—Inflammation of the fib rous Varying disciplines can produce dif ferent joint capsule. This condition usually is pres- joint problems. For example, horses used ent when synovitis occurs. for jumping will tend to have more prob- osteoarthritis—The result of severe joint lems in front leg joints, and horses used for injuries and of injuries that are not treated cutting and reining will tend to have rear on the adequately. Its signs include swelling and leg joint problems. Both will have more pain, plus the progressive loss of articular of a tendency for joint problems than the cartilage on the surface of the bone. This is trail horse or even the endurance horse. a permanent condition that can render the The reason is that the joints are designed These conditions are categorized as fol- horse unsound and unusable. for straight-line movement and not for the lows: Others problems can include bone frag- concussive trauma of landing after a high synovitis—Inflammation of the delicate mentation or fracture in a joint and tearing jump or the torque delivered to hock and synovial membranes. of the ligaments that stabilize the joints. pastern joints from a sliding stop or spin. fBy Les seLLorehandnow With joint injury, there is inflam mation that can stimulate the release of problem he foreleg of the horse is, for agents called free radicals, prostaglandins, the most part, a model of good and cytokines. These agents at tack the ba- Tengineering. It is structured sic components of ar ticular car tilage and in such a fashion that the horse can set in motion a degenerative process that move slowly or at speed with the con- can quickly compromise a horse’s ability cussion of each footfall minimized to perform if untreated. In the process, by a sophisticated shock absorbing there often is a depletion of hyaluronic system. acid that might have to be replenished either via di rect injection into the joint or intravenously. Most of a horse’s weight is carried When a joint is puffy on its forelimbs. and sore, this means Good conforma- joint damage or tion will help disease is present. ensure long-term soundness When a joint is puffy and sore, this means joint damage or disease is present. A veterinarian should be summoned so The system works very well when that the proper treatment can begin im- the horse is doing what nature in- mediately. Often a first-line treatment of tended—wandering about over choice is the application of ice to the in- large expanses, grazing, drinking, jured joint in an effort to immediately re- breed ing, and resting. But today’s duce inflammation. horse often soars over multiple six- foot jumps, runs at speed for a mile Take-Home Message or more around an oval course, The movement of a horse is dependent slides to a stop suddenly and spins, on joints of various types. Proper conforma- or per forms intricate dressage tion is a good deterrent to joint problems, movements. but injury or stress from repeated or hard These disciplines often put undue exercise can cause damage to joints. Unless stress on the legs that can render they are diagnosed and treated early, these even a well-conformed horse un- problems can cripple the horse and end his sound. A horse with improper con- athletic career. h formation is at much greater risk for unsoundness when competing About the Author Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he editor’s Note operates a ranch where he raises horses and livestock. He This is the third in a 12-part series of articles on has authored several fiction and non-fiction books, includ- equine anatomy and physiology. Future topics ing understanding equine Lameness, understanding the include the the hind limb, the hoof, the head and young Horse, and the Journey of the western Horse, neck, the back, muscles, tendons and ligaments, published by Eclipse Press and available at www.Exclusively the digestive system, the circulatory and respira- Equine.com or by calling 800/582-5604. tory systems, and the reproductive system. Dr. roBin Peterson iLLustrations

14 www.TheHorse.com The horse December 2006 December 2006 The horse 15 Capsulitis—Inflammation of the fib rous Varying disciplines can produce dif ferent joint capsule. This condition usually is pres- joint problems. For example, horses used ent when synovitis occurs. for jumping will tend to have more prob- osteoarthritis—The result of severe joint lems in front leg joints, and horses used for injuries and of injuries that are not treated cutting and reining will tend to have rear on the adequately. Its signs include swelling and leg joint problems. Both will have more pain, plus the progressive loss of articular of a tendency for joint problems than the cartilage on the surface of the bone. This is trail horse or even the endurance horse. a permanent condition that can render the The reason is that the joints are designed These conditions are categorized as fol- horse unsound and unusable. for straight-line movement and not for the lows: Others problems can include bone frag- concussive trauma of landing after a high synovitis—Inflammation of the delicate mentation or fracture in a joint and tearing jump or the torque delivered to hock and synovial membranes. of the ligaments that stabilize the joints. pastern joints from a sliding stop or spin. fBy Les seLLorehandnow With joint injury, there is inflam mation that can stimulate the release of problem he foreleg of the horse is, for agents called free radicals, prostaglandins, the most part, a model of good and cytokines. These agents at tack the ba- Tengineering. It is structured sic components of ar ticular car tilage and in such a fashion that the horse can set in motion a degenerative process that move slowly or at speed with the con- can quickly compromise a horse’s ability cussion of each footfall minimized to perform if untreated. In the process, by a sophisticated shock absorbing there often is a depletion of hyaluronic system. acid that might have to be replenished either via di rect injection into the joint or intravenously. Most of a horse’s weight is carried When a joint is puffy on its forelimbs. and sore, this means Good conforma- joint damage or tion will help disease is present. ensure long-term soundness When a joint is puffy and sore, this means joint damage or disease is present. A veterinarian should be summoned so The system works very well when that the proper treatment can begin im- the horse is doing what nature in- mediately. Often a first-line treatment of tended—wandering about over choice is the application of ice to the in- large expanses, grazing, drinking, jured joint in an effort to immediately re- breed ing, and resting. But today’s duce inflammation. horse often soars over multiple six- foot jumps, runs at speed for a mile Take-Home Message or more around an oval course, The movement of a horse is dependent slides to a stop suddenly and spins, on joints of various types. Proper conforma- or per forms intricate dressage tion is a good deterrent to joint problems, movements. but injury or stress from repeated or hard These disciplines often put undue exercise can cause damage to joints. Unless stress on the legs that can render they are diagnosed and treated early, these even a well-conformed horse un- problems can cripple the horse and end his sound. A horse with improper con- athletic career. h formation is at much greater risk for unsoundness when competing About the Author Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he editor’s Note operates a ranch where he raises horses and livestock. He This is the third in a 12-part series of articles on has authored several fiction and non-fiction books, includ- equine anatomy and physiology. Future topics ing understanding equine Lameness, understanding the include the the hind limb, the hoof, the head and young Horse, and the Journey of the western Horse, neck, the back, muscles, tendons and ligaments, published by Eclipse Press and available at www.Exclusively the digestive system, the circulatory and respira- Equine.com or by calling 800/582-5604. tory systems, and the reproductive system. Dr. roBin Peterson iLLustrations

14 www.TheHorse.com The horse December 2006 December 2006 The horse 15 researchers, veterinarians, and horse own- Dem Bones forelimb anatomy ditions and what they might mean, noting Carpus varus—Also called bow legs, this ers in the study of equine limbs is the late Let’s look at each of the forelimb bones, as we do so that few, if any, horses have occurs when one or both knees deviates O.R. Adams’ book Lameness In Horses. traveling from top to bottom. We start perfect forelimb conformation: laterally, or outward, when viewed from with the shoulder bone or scapula. This Toeing out—If this is the case, the horse’s the front. Abnormally high stresses on the No Connections? Shocking! is a broad bone that connects to the next scapula front feet will literally be pointed outward lateral or outer side result from this prob- An interesting aspect of front limb con- in line—the humerus, which is analogous and our superimposed line will run down lem, and toeing in often is also present. struction in the horse is that the front legs to the human upper arm bone. This bone through the inside or medial aspect of the The last two problems occur com monly are not connected to the rest of the skel- angles down and rearward until it joins foot. These horses will put extra stress on in foals, but are usually easily correct ed disciplines. This doesn’t mean a horse with eton. If one were so inclined, one could up with the radius (forearm) at the elbow. the inside of the knees and fetlocks with eith er with rest and trimming/shoeing or poor conformation will always become un- amputate the entire front leg—from scap- The radius extends downward to the knee every stride. Of course, stress increases surgery while the limbs are still growing. sound or lame. What it does mean is that ula (shoulder blade) on down—without or carpus, which compares to the human when the horse travels at speed or lands These are seven basic conformational shoulder joint poor con formation is a warn ing sign that the scalpel ever touching bone. Instead of wrist. One can almost liken the many little after a jump. In addition, as the horse trav- faults that can be observed when viewing something might go awry. bone and joints, the horse’s front legs are bones of the knee to building blocks ar- els, it will tend to wing inward with each the leg from the front. Sometimes they It also should be noted that a horse con nected to its body by a network of mus- ranged in two rows. The radius connects at humerus foot during each stride, particularly at the are combined with other conformational puts more stress on its front legs than its cles, ligaments, and tendons. Basically, the the upper portion of this structure and the trot. When this is the case, the horse is in faults of the front limb, and that increases rear limbs because it carries 60-65% of its horse’s front legs help form a sling that sup- metacarpus (cannon bone) connects to the danger of striking the sesamoid and splint the potential for lameness problems. weight up front. It seems incredible that ports the front part of the animal’s body. lower or distal aspect. The cannon bone ex- elbow joint bones of the opposing limb. Now, let’s step to the side and look at that when a horse is running at speed, there A prime purpose of the front leg is to tends downward to the pastern. Toeing In—As the name implies, this is same front limb. Again, we will superim- is a split second in every stride where all serve as a shock absorber. If the impact The fetlock joint connects the cannon the direct opposite of toeing out, and it of- pose, in our mind’s eye, a vertical line that of the animal’s weight, plus the additional of each stride were transmitted upward with the first of three pastern bones. The ten has less severe consequences. A toed-in runs down the center of the limb perpen- impact involved when running all out, in a straight line, joints, muscles, tendons, first pastern bone is known as the first pha- horse often will paddle, which means the dicular to the ground, reaching the ground lands on one front leg. and perhaps even bones would not remain lanx or P1. It fits into the second pastern feet rotate outward or laterally as it travels, just behind the heel. Here are some poor healthy. The key to proper shock absorp- bone via the pastern joint, with the second radius especially at the trot. This is a waste of en- conformations that might be observed: l eft Stifle Joint: tion here is angle. The proper angle of the bone known as the second phalanx or P2. accessory car- ergy and means the horse does not travel Calf knee—Horse owners familiar with n ormal and with o C d fetlock, for example, makes it possible for The second phalanx fits into the third pha- pal bone forward efficiently. Its danger of self-injury cattle can easily envision this condition. It femur a large portion of the shock forces to be lanx (P3 or coffin bone) at the coffin joint. knee joint or is limited, but this defect does cause addi- also is referred to as “behind at the knee.” carpus carpal or knee dissipated before traveling up to the knee, The coffin bone is housed completely with- bones tional strain on the ligaments of the fetlock The knee appears to bend backward from forearm, and shoulder. The rest of the in the hoof capsule. and pastern joints; problems such as ring- our superimposed line when viewed from patella lateral force is absorbed along the way, but much While the above could be described as splint bone bone and sidebone can result. In this case, the side. These knees place a great deal of trochlear of it is absorbed at the fetlock level. the key bones in the front limb, others when examining the leg from in front, the stress on ligaments and tendons as well as ridge cannon bone of femur serve equally important functions. For ex- fetlock joint bulk of the foot will be inside or at the me- on the knee joint. A calf-kneed horse would The Right Angles ample, just behind the cannon bone, where dial aspect of our superimposed line. be poorly suited for jumping or racing. medial Forelimb angles begin at the shoulder it joins the long pastern bone, are two prox- proximal or first Bench knee—In these horses, the forearm Buck knee—Also called “over at the knee,” trochlear pastern joint phalanx imal sesamoid bones. They serve as pulleys ridge (see illustration at right). If the ani- enters the knee on the medial side and the this is the opposite of calf knee. When of femur mal has good conformation, the for the flexor tendons as the ten dons bend middle or second can non bone exits the knee on the lateral viewed from the side, the knee pro trudes shoulder will be angled back at around the fetlock joint; these tendons help coffin joint phalanx side, so they don’t line up. They are believed over our line as if it is always bent to some an appropriate degree. Just ex- flex the legs and generate propulsion. distal or third phalanx, to be prone to knee in juries or prob lems, degree. It isn’t as severe as calf knee, but is actly what that “appropriate” Another bone completely encapsulated a.k.a. coffin bone especially if ex posed to stressful competi- a definite fault that will put excess stress on degree is will vary from horse by the hoof is the distal sesamoid bone, tion. However, some stud ies have found joints, ligaments, and tendons. to horse, but the angle is key to more commonly called the navicular bone. that mildly affect ed racing Thoroughbreds standing under—In this conformation, the horse’s stride. It is located at the junction of the short pas- meant by those terms. To do that, we must can do quite well, de pending on what other the entire forelimb from elbow on down If the shoulder is aligned appro- tern bone and the coffin bone and provides ex amine a front leg from at least two van- conformational problems are present. is consistently placed back too far under fibula priately, the horse will step out with a another pulley-type surface for the deep tage points—from the front and from the Base-wide—These horses stand with the body, behind our superimposed line. tibia long, even stride that is comfortable for digital flexor tendon as it angles towards side. their hooves farther apart than the legs are Overloading of the front limbs and more lateral trochlear Lateral Trochlear the rider and produces the least amount its end on the bottom of the coffin bone. First, we stand in front of the horse and at the chest. They often have narrow chests, frequent stumbling result. ridgeRidge of of femur Femur withwith OCD OCD of concussion. But if the shoulder angle is Two other bones in the front leg must look at the front leg. In our mind’s eye, we toe out, wing in, and excessively wear the Camped in front—This is the opposite steep, the horse’s stride will be short and be mentioned—the splint bones that ex- will superimpose a vertical line that trav- inner side of the foot. of standing under, with the forelimb from choppy. This will make for an uncomfort- tend downward from the knee. Known as els in a straight path from the point of the Base-narrow—These animals stand with the body to the ground being consistently Osteochondrosis might lead to OCD or subchondral cystic lesions. OCD normally shows up in one able ride, but worst of all, it means the the second and fourth metacarpal (front shoulder down through the middle of the their hooves closer together than the legs placed too far forward—in front of the su- joint rather than multiple joints. However, bilat- front feet will hit the ground more often legs) or metatarsal (hind legs) bones, these forearm, through the middle of the knee, are at the chest. They usually have wide perimposed line. It often occurs with bilat- eral involvement (of both front or hind limbs) over a prescribed course and each time help support the cannon bones. Most au- and down the center of the cannon bone, chests, toe in, paddle out, and wear the eral navicular disease and laminitis. is sufficiently common that the opposite joints they do, the force of concussion will be thorities speculate they are evolutionary fetlock, and hoof. outside of the foot lower than the inside. short, upright pasterns—In this condi- should always be radiographed. greater than for a horse with a properly rem nants from the prehistoric three-toed The purpose of superimposing this line Carpal valgus—Also called knock knees, tion, there is little or no angle to the pas- angled shoulder. This is because the shoul- horse. Splint bones can be fractured or is to determine how much deviation there this angular limb deformity oc curs when tern, which means little dissipation of con- We will take an in-depth look at just der angle dictates other angles involved in broken, causing pain and unsight ly blem- is to one side or the other. If, when we one or both carpi (knees) deviate medially cussion as the horse travels. how the forelimb is constructed, what dissipation of concussion. ishes. study our superimposed line, we find that (inward) when viewed from the front. If Long, sloping pasterns—This can be a constitutes good conformation, and what For example, a straight shoulder nor- it truly does run through the center of the left uncorrected, this results in a great deal severe problem if the pasterns are so long, can go awry when poor conformation is mally means a horse will have a straight Good, Bad, and Ugly limb, we likely have a horse with the basics of stress placed on the ligaments and small sloping, and weak that the fetlock strikes involved. or upright pastern. The straighter the pas- We have mentioned “good” conforma- of good forelimb conformation. bones of the knee, especially on its medial the ground as the horse travels. Neither The information presented comes tern, the less shock absorbed during each tion and “bad” conformation several times But what if it doesn’t? What are we deal- or inner side. Toe ing out often accompa- pastern fault is unique to the forelimbs; from many sources. A key source for stride. in this article. Let’s define just what is ing with? Let’s look at some of these con- nies this problem. they can occur in the hind limbs as well.

16 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 17 researchers, veterinarians, and horse own- Dem Bones forelimb anatomy ditions and what they might mean, noting Carpus varus—Also called bow legs, this ers in the study of equine limbs is the late Let’s look at each of the forelimb bones, as we do so that few, if any, horses have occurs when one or both knees deviates O.R. Adams’ book Lameness In Horses. traveling from top to bottom. We start perfect forelimb conformation: laterally, or outward, when viewed from with the shoulder bone or scapula. This Toeing out—If this is the case, the horse’s the front. Abnormally high stresses on the No Connections? Shocking! is a broad bone that connects to the next scapula front feet will literally be pointed outward lateral or outer side result from this prob- An interesting aspect of front limb con- in line—the humerus, which is analogous and our superimposed line will run down lem, and toeing in often is also present. struction in the horse is that the front legs to the human upper arm bone. This bone through the inside or medial aspect of the The last two problems occur com monly are not connected to the rest of the skel- angles down and rearward until it joins foot. These horses will put extra stress on in foals, but are usually easily correct ed disciplines. This doesn’t mean a horse with eton. If one were so inclined, one could up with the radius (forearm) at the elbow. the inside of the knees and fetlocks with eith er with rest and trimming/shoeing or poor conformation will always become un- amputate the entire front leg—from scap- The radius extends downward to the knee every stride. Of course, stress increases surgery while the limbs are still growing. sound or lame. What it does mean is that ula (shoulder blade) on down—without or carpus, which compares to the human when the horse travels at speed or lands These are seven basic conformational shoulder joint poor con formation is a warn ing sign that the scalpel ever touching bone. Instead of wrist. One can almost liken the many little after a jump. In addition, as the horse trav- faults that can be observed when viewing something might go awry. bone and joints, the horse’s front legs are bones of the knee to building blocks ar- els, it will tend to wing inward with each the leg from the front. Sometimes they It also should be noted that a horse con nected to its body by a network of mus- ranged in two rows. The radius connects at humerus foot during each stride, particularly at the are combined with other conformational puts more stress on its front legs than its cles, ligaments, and tendons. Basically, the the upper portion of this structure and the trot. When this is the case, the horse is in faults of the front limb, and that increases rear limbs because it carries 60-65% of its horse’s front legs help form a sling that sup- metacarpus (cannon bone) connects to the danger of striking the sesamoid and splint the potential for lameness problems. weight up front. It seems incredible that ports the front part of the animal’s body. lower or distal aspect. The cannon bone ex- elbow joint bones of the opposing limb. Now, let’s step to the side and look at that when a horse is running at speed, there A prime purpose of the front leg is to tends downward to the pastern. Toeing In—As the name implies, this is same front limb. Again, we will superim- is a split second in every stride where all serve as a shock absorber. If the impact The fetlock joint connects the cannon the direct opposite of toeing out, and it of- pose, in our mind’s eye, a vertical line that of the animal’s weight, plus the additional of each stride were transmitted upward with the first of three pastern bones. The ten has less severe consequences. A toed-in runs down the center of the limb perpen- impact involved when running all out, in a straight line, joints, muscles, tendons, first pastern bone is known as the first pha- horse often will paddle, which means the dicular to the ground, reaching the ground lands on one front leg. and perhaps even bones would not remain lanx or P1. It fits into the second pastern feet rotate outward or laterally as it travels, just behind the heel. Here are some poor healthy. The key to proper shock absorp- bone via the pastern joint, with the second radius especially at the trot. This is a waste of en- conformations that might be observed: l eft Stifle Joint: tion here is angle. The proper angle of the bone known as the second phalanx or P2. accessory car- ergy and means the horse does not travel Calf knee—Horse owners familiar with n ormal and with o C d fetlock, for example, makes it possible for The second phalanx fits into the third pha- pal bone forward efficiently. Its danger of self-injury cattle can easily envision this condition. It femur a large portion of the shock forces to be lanx (P3 or coffin bone) at the coffin joint. knee joint or is limited, but this defect does cause addi- also is referred to as “behind at the knee.” carpus carpal or knee dissipated before traveling up to the knee, The coffin bone is housed completely with- bones tional strain on the ligaments of the fetlock The knee appears to bend backward from forearm, and shoulder. The rest of the in the hoof capsule. and pastern joints; problems such as ring- our superimposed line when viewed from patella lateral force is absorbed along the way, but much While the above could be described as splint bone bone and sidebone can result. In this case, the side. These knees place a great deal of trochlear of it is absorbed at the fetlock level. the key bones in the front limb, others when examining the leg from in front, the stress on ligaments and tendons as well as ridge cannon bone of femur serve equally important functions. For ex- fetlock joint bulk of the foot will be inside or at the me- on the knee joint. A calf-kneed horse would The Right Angles ample, just behind the cannon bone, where dial aspect of our superimposed line. be poorly suited for jumping or racing. medial Forelimb angles begin at the shoulder it joins the long pastern bone, are two prox- proximal or first Bench knee—In these horses, the forearm Buck knee—Also called “over at the knee,” trochlear pastern joint phalanx imal sesamoid bones. They serve as pulleys ridge (see illustration at right). If the ani- enters the knee on the medial side and the this is the opposite of calf knee. When of femur mal has good conformation, the for the flexor tendons as the ten dons bend middle or second can non bone exits the knee on the lateral viewed from the side, the knee pro trudes shoulder will be angled back at around the fetlock joint; these tendons help coffin joint phalanx side, so they don’t line up. They are believed over our line as if it is always bent to some an appropriate degree. Just ex- flex the legs and generate propulsion. distal or third phalanx, to be prone to knee in juries or prob lems, degree. It isn’t as severe as calf knee, but is actly what that “appropriate” Another bone completely encapsulated a.k.a. coffin bone especially if ex posed to stressful competi- a definite fault that will put excess stress on degree is will vary from horse by the hoof is the distal sesamoid bone, tion. However, some stud ies have found joints, ligaments, and tendons. to horse, but the angle is key to more commonly called the navicular bone. that mildly affect ed racing Thoroughbreds standing under—In this conformation, the horse’s stride. It is located at the junction of the short pas- meant by those terms. To do that, we must can do quite well, de pending on what other the entire forelimb from elbow on down If the shoulder is aligned appro- tern bone and the coffin bone and provides ex amine a front leg from at least two van- conformational problems are present. is consistently placed back too far under fibula priately, the horse will step out with a another pulley-type surface for the deep tage points—from the front and from the Base-wide—These horses stand with the body, behind our superimposed line. tibia long, even stride that is comfortable for digital flexor tendon as it angles towards side. their hooves farther apart than the legs are Overloading of the front limbs and more lateral trochlear Lateral Trochlear the rider and produces the least amount its end on the bottom of the coffin bone. First, we stand in front of the horse and at the chest. They often have narrow chests, frequent stumbling result. ridgeRidge of of femur Femur withwith OCD OCD of concussion. But if the shoulder angle is Two other bones in the front leg must look at the front leg. In our mind’s eye, we toe out, wing in, and excessively wear the Camped in front—This is the opposite steep, the horse’s stride will be short and be mentioned—the splint bones that ex- will superimpose a vertical line that trav- inner side of the foot. of standing under, with the forelimb from choppy. This will make for an uncomfort- tend downward from the knee. Known as els in a straight path from the point of the Base-narrow—These animals stand with the body to the ground being consistently Osteochondrosis might lead to OCD or subchondral cystic lesions. OCD normally shows up in one able ride, but worst of all, it means the the second and fourth metacarpal (front shoulder down through the middle of the their hooves closer together than the legs placed too far forward—in front of the su- joint rather than multiple joints. However, bilat- front feet will hit the ground more often legs) or metatarsal (hind legs) bones, these forearm, through the middle of the knee, are at the chest. They usually have wide perimposed line. It often occurs with bilat- eral involvement (of both front or hind limbs) over a prescribed course and each time help support the cannon bones. Most au- and down the center of the cannon bone, chests, toe in, paddle out, and wear the eral navicular disease and laminitis. is sufficiently common that the opposite joints they do, the force of concussion will be thorities speculate they are evolutionary fetlock, and hoof. outside of the foot lower than the inside. short, upright pasterns—In this condi- should always be radiographed. greater than for a horse with a properly rem nants from the prehistoric three-toed The purpose of superimposing this line Carpal valgus—Also called knock knees, tion, there is little or no angle to the pas- angled shoulder. This is because the shoul- horse. Splint bones can be fractured or is to determine how much deviation there this angular limb deformity oc curs when tern, which means little dissipation of con- We will take an in-depth look at just der angle dictates other angles involved in broken, causing pain and unsight ly blem- is to one side or the other. If, when we one or both carpi (knees) deviate medially cussion as the horse travels. how the forelimb is constructed, what dissipation of concussion. ishes. study our superimposed line, we find that (inward) when viewed from the front. If Long, sloping pasterns—This can be a constitutes good conformation, and what For example, a straight shoulder nor- it truly does run through the center of the left uncorrected, this results in a great deal severe problem if the pasterns are so long, can go awry when poor conformation is mally means a horse will have a straight Good, Bad, and Ugly limb, we likely have a horse with the basics of stress placed on the ligaments and small sloping, and weak that the fetlock strikes involved. or upright pastern. The straighter the pas- We have mentioned “good” conforma- of good forelimb conformation. bones of the knee, especially on its medial the ground as the horse travels. Neither The information presented comes tern, the less shock absorbed during each tion and “bad” conformation several times But what if it doesn’t? What are we deal- or inner side. Toe ing out often accompa- pastern fault is unique to the forelimbs; from many sources. A key source for stride. in this article. Let’s define just what is ing with? Let’s look at some of these con- nies this problem. they can occur in the hind limbs as well.

16 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 17 is balance, with all parts flowing smoothly and cause fewer lameness problems for together so that there is both appropriate the owner. H the propulsion and adequate shock absorp- About the Author tion. Les Sellnow is a free-lance writer based near Riverton, Since no horse has perfect conforma- Wyo. He specializes in articles on equine research, and he tion, it is necessary to rely on experts to de- operates a ranch where he raises horses and livestock. He termine which conformation is best suited has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the to a particular discipline or use. This will young Horse, and the Journey of the western Horse, Take-Home Message enable us to select horses that are more published by Eclipse Press and available at www.Exclusively Perfect engine Equine.com or by calling 800/582-5604. The key to good front limb conformation successful and sounder in their careers, No matter the breed or discipline, good conformation of the hind legs f orelimb C onformation problemS will contribute to more successful performance and a better ride Much as we would like to believe otherwise, NORMAL FRONT END BASE NARROw BASE wiDE By Les seLLnow it is very rare to find a perfectly conformed uch has already been stated in this series about the special con- horse. Most have at least one deviation from cerns involving front limb soundness in the horse since 60-65% what is considered “ideal” conformation, and of the animal’s weight is carried in the front end. This does not many have two or more. Horses can still be M mean that there are no concerns involving the back legs. Far from it. successful riding or working horses with most We can think of equine rear end function in terms of cars and trucks of these abnormalities if they are not very with rear wheel drive. The engine, comprised of muscles fueled by severe. This depends on the particular problem heart and lungs, provides the power, and the back legs are akin to and the horse’s intended use. piston-driven rear wheels. When viewed from either the front or the The pressure and torque placed on the “rear wheels” var- side, a line bisecting the horse’s limb shound ies with the discipline involved. When walking or jogging across be straight. Here, the green lines show the the countryside during a trail ride, the stresses are light and angles of the horses’ bones with normal con- easily handled by a horse with normal back leg conformation. formation and various problems.

KNOCK KNEES BOw LEgS TOED iN TOED OuT BENCH KNEE

NORMAL FRONT END BuCKED KNEE CALF KNEE LONg, wEAK SHORT, uPRigHT PASTERN PASTERN

KNOCK KNEES BOw LEgS TOED iN TOED OuT BENCH KNEE

NORMAL FRONT END BuCKED KNEE CALF KNEE LONg, wEAK SHORT, uPRigHT PASTERN PASTERN

editor’s Note This is the fourth in a 12-part series of articles on equine anatomy and physiology. Future topics include the hoof, the head and neck, the back, muscles, tendons and ligaments, the digestive system, the circulatory and respiratory systems, and the reproductive system. Dr. roBin Peterson iLLustrations 18 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 19 normal and problematiC hind limb C onformation hind limb anatomy knee on the front leg in that it is comprised one back foot pretty much anchored in When a horse’s hind limbs NORMAL HiND END NORMAL HiND END tuber sacrale of a number of bones—six to be exact. A place as the horse does 360-degree turns, aren’t aligned as they should difference between hock and knee is the often at speed. be, some internal structures fact that the hock bones lack the degree are stressed more heavily, of motion noted in the bones of the knee. Different Stresses ilium resulting in a greater risk of Like the knee joint, the hock joint is held Back to English riding, we find that dres- pain and lameness. For ex- together by a complex set of ligaments that sage horses also place added strain on the ample, the cow-hocked horse enable it to function. The prime function of rear end as they perform intricate patterns. However, if the discipline happens to be will place extra strain in the the hock is to provide rear leg propulsion. The same is true of the jumper. In that dis- hip joint cutting or reining with the Western horse medial side (inside) of his The bones of the hock include: Calca- cipline, we generally think in terms of more or dressage or five-gaited action with the hocks, resulting in a greater neus and talus on top of the central tarsal stress being placed on the front end as the ischiatic femur tuberosity show horse, it is an entirely different mat- risk of bone spavin, and bone, third tarsal bone, first and second horse lands after taking a jump. However, patella ter. Although different in nature, these straight hocks will not be able tarsal bones (which are fused), and the in order for the horse to land it has to take fourth tarsal bone. four disciplines all put high demands on to absorb as much shock as off, and it is the rear end that provides pro- stifle the horse’s rear end. they should. The horse’s stifle joint is the largest single pulsion for a soaring jump. joint It should also be remembered that, in ad- joint in its body. One of its functions is to While we generally don’t think that dition to being the prime source of propul- STRAigHT HOCKS COw HOCKS BOw HOCKS cause the rear limb to become rigid when much stress is placed on the rear end of sion, the back legs also serve as the horse’s the foot is on the ground. This is controlled trail horses, being ridden either in English brakes. Again, the stress put on those via contraction of muscles above the patel- or Western tack, there are times when the brakes varies with the discipline. It is vast- la, which releases the stay apparatus, and demands are high. An example would be tuber ly different, for example, in a reining horse is the equivalent of a human’s kneecap. climbing a steep hill or mountain where a calcanei than it is for one competing in dressage. The type of activity with which the horse strong rear end is required for propulsion tibia We’ll take a look at how Nature has de- is involved has a great deal to do with the upward as well as forward. When descend- hock signed the rear portion of the horse’s anato- stresses and pressures that are placed on ing a steep slope, a strong rear end and joint my, especially the leg, in an effort to under- the hocks. Walking, jogging, or even gallop- sound legs also are needed, this time to pro- tarsal or hock bones stand why the animal can do what it does. ing puts little undue stress on the back legs vide braking capability that allows a horse We also will take a look at some of the prob- in general and the hocks in particular. to travel downward slowly and safely. cannon bone or lems that can develop in improperly con- However, when one ups the ante with What this all means is that, regardless of metatarsus splint formed legs as a result of these stresses. some activities, it all changes. One type of discipline, we want a horse to have excel- fetlock joint bone An excellent source on equine anatomy stress, for example, is placed on the hocks lent rear leg conformation so that it can tol- proximal or first phalanx as it pertains to feet and legs is the fourth by five-gaited horses, particularly Saddle- erate the demands placed on it by respec- pastern joint edition of Adams’ Lameness in Horses, edit- breds. When performing at the signature tive disciplines and still remain sound. middle or ed by Ted Stashak, DVM, MS, and featuring SiCKLE HOCKS BASE-wiDE BASE-NARROw gaits of rack and slow gait, the horse is mov- (A discussion of the roles played by mus- second phalanx seven experts in the field as contributors. ing in a four-beat rhythm. This means that cles, tendons, and ligaments to enable rear coffin joint each leg strikes the ground separately. Put leg propulsion as well as braking action distal or third phalanx, Start at the Top another way, it means that all of the horse’s will appear in future articles.) a.k.a. coffin bone We will begin our visual dissection of weight is balanced on one leg during each the posterior portion of the horse’s anato- complete stride. Add to this the fact that What to Look For my at the top, or spine, and work our way five-gaited horses shift weight to the rear When examining the horse’s back legs, If we call into play again our imaginary downward. Connecting to the spine is the and elevate the front end while slow gaiting we want to look at the limbs from the plumb line, we should be able to start it at ilium, the largest of three bones in the an- and racking, and one can quickly conclude rear and the side. We’ll start with a view the rear of the buttocks and drop a straight imal’s pelvis. The ilium angles down and that the stresses and strains placed on the from the rear. We want to see a horse that line downward to the hock and along the rearward, and it attaches to the femur or rear end multiply. is evenly balanced. This means that the cannon bone until it reaches the ground thigh bone. The angular shape of the pelvis When we consider some of the Western distance between its thigh area, as well as three to four inches behind the heel. determines what type of croup the horse classes, the stress and strain placed on the between the hocks, should be about the What we are describing is ideal rear leg has—flat or sloped. rear end change in form, but are equally se- same as the distance between the rear feet conformation. Unfortunately, few horses The femur angles slightly forward and vere. The cutting horse, for example, works as they rest on the ground. The back legs have perfect leg conformation, front or connects with the stifle, forming one of the almost completely off the rear end. Its back should be straight from this viewpoint. If a rear. Some deviations are minor and oth- more important joints in the rear leg ap- that are important to the function of the leg. the horse’s ability to propel itself forward, legs serve as both propulsion and brakes vertical line were drawn on a photo taken ers are major. The type of deviation and paratus. Connecting at the stifle joint, as Where the cannon bone joins the long pas- brake to a halt, and move backward. as the horse slides to a stop, then shoots from behind, the line would go as straight the severity goes a long way in determining we continue our journey downward or dis- tern bone, two small bones—the proximal If one were to rate them as to impor- forward or sideways as the cow turns and as a plumb line from the center of the but- whether the horse will remain sound. tally, is the tibia, which connects with the sesamoids—lie on the back side of the can- tance in this regard, the hock would per- tries to escape. The process of turning while tocks, downward through the center of the Here are the four most common de- hock. Emerging from the distal portion of non bone and act as pulleys for the flexor haps be placed at the head of the list. The weight is suspended over the rear often entire rear leg, all the way distally through viations in rear leg conformation that can the hock is the metatarsus or rear cannon tendons. And where the short pastern and propelling force is transmitted by tendons places terrific torque on the hocks and can pastern and hoof to ground level. cause problems, particularly if they are se- bone. This bone continues downward un- coffin bone join, a distal sesamoid bone, or passing over the hocks, delivering energy lead to soundness problems such as arthri- Now let’s take a step to the side. From vere: til it connects with the long pastern bone, navicular bone, acts in the same manner. from the muscles for forward propulsion. tis in the hock joint. this viewpoint, we must keep in mind Cow-hocked—With this condition, when which connects with the short pastern On the other hand, the stifle serves much The reining horse also places stress and proper angle. The angle of the stifle and looking at the horse from the rear, the bone, which connects with the coffin bone. Where Does it Hurt? the same function as the human knee. strain on the hocks during its pattern. hock should be neither too straight nor too distance between the feet on the ground As with the foreleg discussion (see www. The two key places where rear leg lame- As mentioned earlier, the hock, or tarsal There will be sliding stops, with most of angular, but should present a well-balanced will be greater than the distance between TheHorse.com.aspx?id=6623), there are ness problems are apt to develop are the joint, is where the tibia joins with the meta- the animal’s weight transferred to the rear picture with muscles running smoothly the hocks. A mildly cow-hocked horse can several small bones in the lower hind limb stifle and the hock. Both play key roles in tarsal bone. The hock is a like the horse’s leg apparatus, and there will be spins, with down the leg to the hock. perform in most disciplines without severe

20 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 21 normal and problematiC hind limb C onformation hind limb anatomy knee on the front leg in that it is comprised one back foot pretty much anchored in When a horse’s hind limbs NORMAL HiND END NORMAL HiND END tuber sacrale of a number of bones—six to be exact. A place as the horse does 360-degree turns, aren’t aligned as they should difference between hock and knee is the often at speed. be, some internal structures fact that the hock bones lack the degree are stressed more heavily, of motion noted in the bones of the knee. Different Stresses ilium resulting in a greater risk of Like the knee joint, the hock joint is held Back to English riding, we find that dres- pain and lameness. For ex- together by a complex set of ligaments that sage horses also place added strain on the ample, the cow-hocked horse enable it to function. The prime function of rear end as they perform intricate patterns. However, if the discipline happens to be will place extra strain in the the hock is to provide rear leg propulsion. The same is true of the jumper. In that dis- hip joint cutting or reining with the Western horse medial side (inside) of his The bones of the hock include: Calca- cipline, we generally think in terms of more or dressage or five-gaited action with the hocks, resulting in a greater neus and talus on top of the central tarsal stress being placed on the front end as the ischiatic femur tuberosity show horse, it is an entirely different mat- risk of bone spavin, and bone, third tarsal bone, first and second horse lands after taking a jump. However, patella ter. Although different in nature, these straight hocks will not be able tarsal bones (which are fused), and the in order for the horse to land it has to take fourth tarsal bone. four disciplines all put high demands on to absorb as much shock as off, and it is the rear end that provides pro- stifle the horse’s rear end. they should. The horse’s stifle joint is the largest single pulsion for a soaring jump. joint It should also be remembered that, in ad- joint in its body. One of its functions is to While we generally don’t think that dition to being the prime source of propul- STRAigHT HOCKS COw HOCKS BOw HOCKS cause the rear limb to become rigid when much stress is placed on the rear end of sion, the back legs also serve as the horse’s the foot is on the ground. This is controlled trail horses, being ridden either in English brakes. Again, the stress put on those via contraction of muscles above the patel- or Western tack, there are times when the brakes varies with the discipline. It is vast- la, which releases the stay apparatus, and demands are high. An example would be tuber ly different, for example, in a reining horse is the equivalent of a human’s kneecap. climbing a steep hill or mountain where a calcanei than it is for one competing in dressage. The type of activity with which the horse strong rear end is required for propulsion tibia We’ll take a look at how Nature has de- is involved has a great deal to do with the upward as well as forward. When descend- hock signed the rear portion of the horse’s anato- stresses and pressures that are placed on ing a steep slope, a strong rear end and joint my, especially the leg, in an effort to under- the hocks. Walking, jogging, or even gallop- sound legs also are needed, this time to pro- tarsal or hock bones stand why the animal can do what it does. ing puts little undue stress on the back legs vide braking capability that allows a horse We also will take a look at some of the prob- in general and the hocks in particular. to travel downward slowly and safely. cannon bone or lems that can develop in improperly con- However, when one ups the ante with What this all means is that, regardless of metatarsus splint formed legs as a result of these stresses. some activities, it all changes. One type of discipline, we want a horse to have excel- fetlock joint bone An excellent source on equine anatomy stress, for example, is placed on the hocks lent rear leg conformation so that it can tol- proximal or first phalanx as it pertains to feet and legs is the fourth by five-gaited horses, particularly Saddle- erate the demands placed on it by respec- pastern joint edition of Adams’ Lameness in Horses, edit- breds. When performing at the signature tive disciplines and still remain sound. middle or ed by Ted Stashak, DVM, MS, and featuring SiCKLE HOCKS BASE-wiDE BASE-NARROw gaits of rack and slow gait, the horse is mov- (A discussion of the roles played by mus- second phalanx seven experts in the field as contributors. ing in a four-beat rhythm. This means that cles, tendons, and ligaments to enable rear coffin joint each leg strikes the ground separately. Put leg propulsion as well as braking action distal or third phalanx, Start at the Top another way, it means that all of the horse’s will appear in future articles.) a.k.a. coffin bone We will begin our visual dissection of weight is balanced on one leg during each the posterior portion of the horse’s anato- complete stride. Add to this the fact that What to Look For my at the top, or spine, and work our way five-gaited horses shift weight to the rear When examining the horse’s back legs, If we call into play again our imaginary downward. Connecting to the spine is the and elevate the front end while slow gaiting we want to look at the limbs from the plumb line, we should be able to start it at ilium, the largest of three bones in the an- and racking, and one can quickly conclude rear and the side. We’ll start with a view the rear of the buttocks and drop a straight imal’s pelvis. The ilium angles down and that the stresses and strains placed on the from the rear. We want to see a horse that line downward to the hock and along the rearward, and it attaches to the femur or rear end multiply. is evenly balanced. This means that the cannon bone until it reaches the ground thigh bone. The angular shape of the pelvis When we consider some of the Western distance between its thigh area, as well as three to four inches behind the heel. determines what type of croup the horse classes, the stress and strain placed on the between the hocks, should be about the What we are describing is ideal rear leg has—flat or sloped. rear end change in form, but are equally se- same as the distance between the rear feet conformation. Unfortunately, few horses The femur angles slightly forward and vere. The cutting horse, for example, works as they rest on the ground. The back legs have perfect leg conformation, front or connects with the stifle, forming one of the almost completely off the rear end. Its back should be straight from this viewpoint. If a rear. Some deviations are minor and oth- more important joints in the rear leg ap- that are important to the function of the leg. the horse’s ability to propel itself forward, legs serve as both propulsion and brakes vertical line were drawn on a photo taken ers are major. The type of deviation and paratus. Connecting at the stifle joint, as Where the cannon bone joins the long pas- brake to a halt, and move backward. as the horse slides to a stop, then shoots from behind, the line would go as straight the severity goes a long way in determining we continue our journey downward or dis- tern bone, two small bones—the proximal If one were to rate them as to impor- forward or sideways as the cow turns and as a plumb line from the center of the but- whether the horse will remain sound. tally, is the tibia, which connects with the sesamoids—lie on the back side of the can- tance in this regard, the hock would per- tries to escape. The process of turning while tocks, downward through the center of the Here are the four most common de- hock. Emerging from the distal portion of non bone and act as pulleys for the flexor haps be placed at the head of the list. The weight is suspended over the rear often entire rear leg, all the way distally through viations in rear leg conformation that can the hock is the metatarsus or rear cannon tendons. And where the short pastern and propelling force is transmitted by tendons places terrific torque on the hocks and can pastern and hoof to ground level. cause problems, particularly if they are se- bone. This bone continues downward un- coffin bone join, a distal sesamoid bone, or passing over the hocks, delivering energy lead to soundness problems such as arthri- Now let’s take a step to the side. From vere: til it connects with the long pastern bone, navicular bone, acts in the same manner. from the muscles for forward propulsion. tis in the hock joint. this viewpoint, we must keep in mind Cow-hocked—With this condition, when which connects with the short pastern On the other hand, the stifle serves much The reining horse also places stress and proper angle. The angle of the stifle and looking at the horse from the rear, the bone, which connects with the coffin bone. Where Does it Hurt? the same function as the human knee. strain on the hocks during its pattern. hock should be neither too straight nor too distance between the feet on the ground As with the foreleg discussion (see www. The two key places where rear leg lame- As mentioned earlier, the hock, or tarsal There will be sliding stops, with most of angular, but should present a well-balanced will be greater than the distance between TheHorse.com.aspx?id=6623), there are ness problems are apt to develop are the joint, is where the tibia joins with the meta- the animal’s weight transferred to the rear picture with muscles running smoothly the hocks. A mildly cow-hocked horse can several small bones in the lower hind limb stifle and the hock. Both play key roles in tarsal bone. The hock is a like the horse’s leg apparatus, and there will be spins, with down the leg to the hock. perform in most disciplines without severe

20 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 21 A look at the structures that make the horse interfering. horse. Rarely is a horse with this confor- Bow-hocked—This is the reverse of the mational fault a good athlete. The reason up the horse’s foot, inside and out condition described above. Here, when is quite basic—the horse is unable to make tthehe looking at the horse from the rear, the dis- proper use of its muscles in either propel- tance between the back feet will be less than ling itself forward or braking to a stop. the distance between the hocks. While nei- sickle-hocked—When we look at a well- ther condition is desirable, base-narrow of- conformed horse from the side, we are ten presents more of a risk to the horse than able to drop our imaginary plumb line stress. However, if the deviation is exagger- base-wide. With hocks that are far apart, and it will travel vertically along the rear ated, undue pressure will be placed on the extreme strain is placed on the joint with of the cannon bone, hitting the ground hock joint (especially the medial or inside each stride and lameness can quickly result behind the rear hoof. With the sickle- EquineEquineBy Les seLLnow FootFoot aspect) with each stop or strong propulsion in a demanding discipline. There is still hocked horse, there will be space between forward, and there is the added danger of another downside for the base-narrow our plumb line and the rear cannon bone, almost from the upper point of the hock downward. A severe deviation with this condition places a great deal of stress on the rear of the hock and can quickly bring unsoundness. It should be kept in mind that in some breeds and disciplines—in particular draft horses for pulling—this conformation is preferred. straight behind—This the opposite of sickle-hocked. In this case there is very little angulation of the femur and the tibia. This condition is capable of placing heavy stress on the stifle joint and the hock. When these horses are used for roping, cutting, or reining, they are prone to injury because the rear legs are incapable of properly using muscles that are designed to help absorb concussion. he equine lexicon is filled with clichés about the equine Back to the Top foot. Most horse owners have heard them all. “No foot, Early on we mentioned that the shape or Tno horse...The foot is the horse’s foundation...For want angulation of the horse’s pelvis determines of a shoe...” The list goes on. Without sound feet, a horse croup conformation. The conformation can’t move freely, and a horse whose movement is hindered can range from straight to severely sloped, becomes a predator’s meal in the wild and a liability to its with a variety of degrees in between. The owner in a domestic setting. slope of the croup helps to determine the A quick outward glance at a horse’s foot gives little clue as discipline for which the particular horse is to its complex nature. On the surface, we see a hard, horny designed. As a general rule, horses with a substance called the hoof wall and nothing more. Beneath sloped croup will perform well in cutting, that hard exterior, however, is a sophisticated arrangement reining, and roping, and horses with level of bones, tendons, ligaments, nerves, blood vessels, and sen- croups—such as the Saddlebred—are more sitive tissue. When this amalgamation of parts is properly apt to show up in gaited and fine harness assembled and functioning well, it is one of Nature’s master- classes or sometimes as racehorses. pieces. When something goes awry, however, the effect can be akin to an explosion in a closed room. Take-Home Message No matter what the breed of horse and no matter what the discipline he performs, good rear leg conformation is highly important if a horse is to be a successful perform- er and remain sound. H About the Author Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he editor’s Note operates a ranch where he raises horses and livestock. He This is the fifth in a 12-part series of articles on has authored several fiction and non-fiction books, includ- equine anatomy and physiology. Future topics ing understanding equine Lameness, understanding the include the head and neck, the back, muscles, young Horse, and the Journey of the western Horse, tendons and ligaments, the digestive system, published by Eclipse Press and available at www.Exclusively the circulatory and respiratory systems, and the Equine.com or by calling 800/582-5604. reproductive system. Dr. roBin Peterson iLLustrations

22 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 23 A look at the structures that make the horse interfering. horse. Rarely is a horse with this confor- Bow-hocked—This is the reverse of the mational fault a good athlete. The reason up the horse’s foot, inside and out condition described above. Here, when is quite basic—the horse is unable to make tthehe looking at the horse from the rear, the dis- proper use of its muscles in either propel- tance between the back feet will be less than ling itself forward or braking to a stop. the distance between the hocks. While nei- sickle-hocked—When we look at a well- ther condition is desirable, base-narrow of- conformed horse from the side, we are ten presents more of a risk to the horse than able to drop our imaginary plumb line stress. However, if the deviation is exagger- base-wide. With hocks that are far apart, and it will travel vertically along the rear ated, undue pressure will be placed on the extreme strain is placed on the joint with of the cannon bone, hitting the ground hock joint (especially the medial or inside each stride and lameness can quickly result behind the rear hoof. With the sickle- EquineEquineBy Les seLLnow FootFoot aspect) with each stop or strong propulsion in a demanding discipline. There is still hocked horse, there will be space between forward, and there is the added danger of another downside for the base-narrow our plumb line and the rear cannon bone, almost from the upper point of the hock downward. A severe deviation with this condition places a great deal of stress on the rear of the hock and can quickly bring unsoundness. It should be kept in mind that in some breeds and disciplines—in particular draft horses for pulling—this conformation is preferred. straight behind—This the opposite of sickle-hocked. In this case there is very little angulation of the femur and the tibia. This condition is capable of placing heavy stress on the stifle joint and the hock. When these horses are used for roping, cutting, or reining, they are prone to injury because the rear legs are incapable of properly using muscles that are designed to help absorb concussion. he equine lexicon is filled with clichés about the equine Back to the Top foot. Most horse owners have heard them all. “No foot, Early on we mentioned that the shape or Tno horse...The foot is the horse’s foundation...For want angulation of the horse’s pelvis determines of a shoe...” The list goes on. Without sound feet, a horse croup conformation. The conformation can’t move freely, and a horse whose movement is hindered can range from straight to severely sloped, becomes a predator’s meal in the wild and a liability to its with a variety of degrees in between. The owner in a domestic setting. slope of the croup helps to determine the A quick outward glance at a horse’s foot gives little clue as discipline for which the particular horse is to its complex nature. On the surface, we see a hard, horny designed. As a general rule, horses with a substance called the hoof wall and nothing more. Beneath sloped croup will perform well in cutting, that hard exterior, however, is a sophisticated arrangement reining, and roping, and horses with level of bones, tendons, ligaments, nerves, blood vessels, and sen- croups—such as the Saddlebred—are more sitive tissue. When this amalgamation of parts is properly apt to show up in gaited and fine harness assembled and functioning well, it is one of Nature’s master- classes or sometimes as racehorses. pieces. When something goes awry, however, the effect can be akin to an explosion in a closed room. Take-Home Message No matter what the breed of horse and no matter what the discipline he performs, good rear leg conformation is highly important if a horse is to be a successful perform- er and remain sound. H About the Author Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he editor’s Note operates a ranch where he raises horses and livestock. He This is the fifth in a 12-part series of articles on has authored several fiction and non-fiction books, includ- equine anatomy and physiology. Future topics ing understanding equine Lameness, understanding the include the head and neck, the back, muscles, young Horse, and the Journey of the western Horse, tendons and ligaments, the digestive system, published by Eclipse Press and available at www.Exclusively the circulatory and respiratory systems, and the Equine.com or by calling 800/582-5604. reproductive system. Dr. roBin Peterson iLLustrations

22 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 23 are included in breeding programs because combined laminae bear much of the weight band is serious, it can result in permanent The Skeletal System b oneS and StruC tureS of the foot of their talent and capabilities in the show of the horse. disfigurement of the hoof and, in some cas- The bones of the foot provide Part 5 deep ditial ring or on the racetrack. As a result, special The junction between the laminae of the es, disrupt proper hoof growth to the point framework and facilitate locomo- P1 flexor tendon care sometimes becomes the norm in order wall and the tubules of the sole is known as where the horse is no longer usable. tion. Nature did an excellent job (DDFT) to keep these hooves and feet functional. the white line. Time to learn another term—corium. in designing the bones. They had collateral ligaments of the The hoof wall is com posed of three dis- Let’s pause for a review of terms. The ex- Understanding its role helps to understand to be light enough to facilitate easy P2 navicular bone That hard, horny hoof wall is not mal- tinct layers. The outer layer is the periople ternal surface at the front of the foot is its how the foot is nourished. The corium is movement, yet strong enough to leable. When an injury or systemic insult (like the human cuticle) and stratum tec- dorsal surface, and the surface facing the a modified vascular (supplied with blood sustain the rigors of weight-bear- navicular causes blood vessels to expand or tissues torium. The periople extends about three- ground is the solar surface. On the front vessels) tissue that is divided into five parts. ing and concussion. When all goes bone to swell, there is no room to accommodate fourths of an inch below the coronet, ex- leg, the caudal (rear) aspect of the foot is First is the perioplic corium, which is a well, they fulfill their roles admi- enlargement of any kind and something cept at the heels, where it caps the bulbs of its palmar surface. In the rear leg this is narrow band lying in the perioplic groove rably. However, when something navicular impar must give. the heels. The coronet encircles the upper referred to as the plantar surface. Medial above the coronary border of the wall. Its goes awry with the bones, the re- ligament We will examine the anatomy of the foot area of the hoof and is the point of demar- (inside) is the term for the portion of the job is to distribute nourishment around the sult can be devastating lameness DDFT in this article. Once again, we use a vari- cation between the skin and the beginning foot nearest the foot on the opposite side. top of the hoof wall. Second is the coro- that is difficult to treat because P3 insertion on P3 ety of sources, but two deserve additional of the hoof wall. The stratum tectorium, Lateral (outside) is the term for the portion nary corium, which, with the perioplic co- of their location inside the horny mention. They are Doug Butler, PhD, Cer- much like the human fingernail, extends of the foot farthest away. rium, helps to form the coronary band. It hoof wall. frog tified Journeyman Farrier, Fellow of the down to the bottom of the foot. It is a thin On all surfaces of the hoof wall are furnishes the bulk of nutrition to the hoof The three bones of the foot are Worshipful Company of Farriers, of Colo- layer of horny scales—hardened cells— small, thin, generally parallel lines that wall and is responsible for growth of the the distal end of the short pas- coffin bone (P3) rado, a lecturer, author, and consultant; that provides the hard, glossy-appearing reach from the coronet to the solar surface. wall. Third is the laminar corium that is at- tern bone, also known as second and David Hood, DVM, PhD, a professor surface below the periople. It is composed These lines are the tubules of the wall. The tached to the coffin bone and nourishes the phalanx (P2) or middle phalanx at Texas A&M University who has been of keratinized epithelial cells that are sol- tubules are constructed in such a way that dermal laminae, the epidermal laminae of (which extends distally from its connec- The coronary cushion is the elastic por- involved in that institution’s Hoof Project. idly cemented together with keratin. One they resist compression of the hoof wall the wall, and the inter-laminar horn of the tion with the pastern bone or first pha- tion of the coronary band. It is a fibro-fatty Information from these researchers comes of its tasks is to protect the hoof wall when the horse’s foot bears weight. white line. Fourth is the sole corium, which lanx (P1); the coffin bone, also known as cushion that is thickest in the center and from past interviews and papers they have from drying out. The hoof wall should be Beneath the surface of the coronet is the is composed of fine hair-like papillae over the third phalanx (P3) or distal phalanx thinnest at the quarters where it attaches authored. Other infor- the entire inner surface of the sole. These (which extends distally from the short to the lateral cartilage. It then widens out mation comes from a internal foot S truC tureS papillae furnish nourishment and growth pastern bone); and the navicular bone, and thickens to form the base of the bulbs variety of papers and LAMiNAE THE CORONET to the sole. Fifth is the frog corium, which also known as the distal sesamoid bone, of the heel, where it blends in with the digi- textbooks. skin/dermis is similar in structure to the sole corium located behind and distal to the short tal cushion. The coronary cushion helps in laminar corium (corim of the skin) It should be noted secondary connective tissue and furnishes nourishment and growth to pastern bone and behind and proxi- the reduction and transfer of compression lamellae that hoof and foot are skin/epidermis the frog. mal to the coffin bone. The bones of the between the hoof wall and the coffin bone not synonymous. The extensor tendon Back to the parts of the foot that are foot and leg are connected by joints and as well as other internal foot parts. perioplic corium hoof or hoof wall, gen- primary readily visible. On the solar surface is the ligaments, so an injury to one can have a The inner foot is serviced by a blood sup- erally speaking, is the lamellae periople sole. The structure of the sole is similar to negative effect on the others. ply that is pumped by the heart through P2 three-layered outer coronary corium that of the wall, with tubules running verti- the arteries to the foot and is assisted in its surface of the foot. coronary band cally as formed by the papillae of the sole Soft Tissues return to the heart by a pumping mecha- The foot, on the other stratum corium. These tubules curl near the ground There are two key tendons within the nism within the foot facilitated by com- hand, includes the lamellae coffin germinativum P3 surface, which accounts for the self-limit- foot. The extensor tendon attaches to the pression involving a complex network of (stratum bone—P3 of coronary band hoof and all the bones, lamellatum) ing growth of the sole and causes shedding. front of the coffin bone and the deep digital veins whenever the horse bears weight blood vessels, liga- hoof wall The sole is not designed to constantly bear flexor tendon attaches to the bottom of the on the foot. They lymphatic system of the ments, tendons, and (stratum weight from the ground surface, but it is coffin bone. limbs also requires this pumping action to tectorium) nerves therein. hoof wall designed to bear internal weight. The navicular bursa is positioned be- move fluids. This is one reason that a horse (stratum medium) hoof wall An integral part of the foot is the frog, tween the deep digital flexor tendon and standing still for a long time will “stock (stratum The Outer Hoof medium) a wedge-shaped mass that occupies angles the flexor surface of the navicular bone and up” because fluids in the legs are not being We begin with that bounded by the bars and the sole. The frog helps reduce concussion on the bone. An- pumped back up the limbs by cycles of foot rather innocuous-ap- lamellae is divided into the apex, which is the for- other inner foot structure that helps absorb loading and unloading. (stratum lamellatum) laminar pearing exterior hoof corium ward-most point; the base, which is the concussion is the digital cushion located hoof wall wall. It plays a com- (stratum tectorium) rear portion; and the frog stay, which is the between the distal coffin bone and the Take-Home Message plicated role to house central ridge. The frog is about 50% water sole. The digital cushion is a wedge-shaped Because the foot plays such a key role in and protect the sensi- and is quite soft. structure with a fibro-fatty composition. It the horse’s ability to survive and function, tive inner foot, support The frog serves as a shock absorber in is very elastic and has very few blood ves- we will end this dissertation on the anat- weight, resist wear, conduct moisture, and approximately 25% water. coronary band. It is the primary growth two ways. First, it helps absorb concus- sels or nerves. When the digital cushion is omy of the foot with the oldest of clichés: absorb shock. The middle layer of the hoof wall com- and nutritional source for the hoof wall. sive force from the ground and, second, compressed by the pastern bones and frog “No foot, no horse.” H In order to accomplish these tasks, the prises the bulk of the wall and is the dens- Within this structure lies a massive supply it acts as a stop that redirects concussive with weight bearing, it absorbs shock, cush- hoof wall and the foot must be healthy. It est portion. The inner layer is the laminar of blood vessels that feed the hoof. These force coming down from the bony column ions the bones, and is divided by the frog’s About the Author is at this point that the owner or caretaker layer. It is concave from side to side and blood vessels, combined with nerves, form through the lateral cartilages and the hoof. exterior spine so that it is forced outward Les Sellnow is a free-lance writer based near Riverton, plays a role. Because we have the horse in bears a multitude of primary and second- a sensitive layer that is attached to the in- The heels of the hoof form the most cau- and obliquely upward against the lateral Wyo. He specializes in articles on equine research, and he an environment of our choosing, the natural ary leaf-like laminae, which attach the cof- side of the hoof wall and the third phalanx dal part of the bearing surface of the hoof cartilages. The lateral cartilages are part operates a ranch where he raises horses and livestock. He selection process does not come into play. fin bone to the inside of the hoof wall, simi- (coffin bone). wall. There the wall makes an acute change fibrous tissue and part hyaline cartilage. has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the In the wild, a horse with poor feet didn’t lar to Velcro. There are some 600 primary Injury to the coronary band can have a in direction, turning back toward the toe. They slope upward and backward from the young Horse, and the Journey of the western Horse, survive and its genes were not passed on. laminae, each of which bears 100 or more serious negative effect on hoof growth and The portions that turn toward the toe are wings of the coffin bone and reach above published by Eclipse Press and available at www.Exclusively Not so today. Some horses with horrid feet secondary laminae on its surface. These development. If the injury to the coronary the bars of the foot. the margin of the coronary band. Equine.com or by calling 800/582-5604.

24 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 25 are included in breeding programs because combined laminae bear much of the weight band is serious, it can result in permanent The Skeletal System b oneS and StruC tureS of the foot of their talent and capabilities in the show of the horse. disfigurement of the hoof and, in some cas- The bones of the foot provide Part 5 deep ditial ring or on the racetrack. As a result, special The junction between the laminae of the es, disrupt proper hoof growth to the point framework and facilitate locomo- P1 flexor tendon care sometimes becomes the norm in order wall and the tubules of the sole is known as where the horse is no longer usable. tion. Nature did an excellent job (DDFT) to keep these hooves and feet functional. the white line. Time to learn another term—corium. in designing the bones. They had collateral ligaments of the The hoof wall is com posed of three dis- Let’s pause for a review of terms. The ex- Understanding its role helps to understand to be light enough to facilitate easy P2 navicular bone That hard, horny hoof wall is not mal- tinct layers. The outer layer is the periople ternal surface at the front of the foot is its how the foot is nourished. The corium is movement, yet strong enough to leable. When an injury or systemic insult (like the human cuticle) and stratum tec- dorsal surface, and the surface facing the a modified vascular (supplied with blood sustain the rigors of weight-bear- navicular causes blood vessels to expand or tissues torium. The periople extends about three- ground is the solar surface. On the front vessels) tissue that is divided into five parts. ing and concussion. When all goes bone to swell, there is no room to accommodate fourths of an inch below the coronet, ex- leg, the caudal (rear) aspect of the foot is First is the perioplic corium, which is a well, they fulfill their roles admi- enlargement of any kind and something cept at the heels, where it caps the bulbs of its palmar surface. In the rear leg this is narrow band lying in the perioplic groove rably. However, when something navicular impar must give. the heels. The coronet encircles the upper referred to as the plantar surface. Medial above the coronary border of the wall. Its goes awry with the bones, the re- ligament We will examine the anatomy of the foot area of the hoof and is the point of demar- (inside) is the term for the portion of the job is to distribute nourishment around the sult can be devastating lameness DDFT in this article. Once again, we use a vari- cation between the skin and the beginning foot nearest the foot on the opposite side. top of the hoof wall. Second is the coro- that is difficult to treat because P3 insertion on P3 ety of sources, but two deserve additional of the hoof wall. The stratum tectorium, Lateral (outside) is the term for the portion nary corium, which, with the perioplic co- of their location inside the horny mention. They are Doug Butler, PhD, Cer- much like the human fingernail, extends of the foot farthest away. rium, helps to form the coronary band. It hoof wall. frog tified Journeyman Farrier, Fellow of the down to the bottom of the foot. It is a thin On all surfaces of the hoof wall are furnishes the bulk of nutrition to the hoof The three bones of the foot are Worshipful Company of Farriers, of Colo- layer of horny scales—hardened cells— small, thin, generally parallel lines that wall and is responsible for growth of the the distal end of the short pas- coffin bone (P3) rado, a lecturer, author, and consultant; that provides the hard, glossy-appearing reach from the coronet to the solar surface. wall. Third is the laminar corium that is at- tern bone, also known as second and David Hood, DVM, PhD, a professor surface below the periople. It is composed These lines are the tubules of the wall. The tached to the coffin bone and nourishes the phalanx (P2) or middle phalanx at Texas A&M University who has been of keratinized epithelial cells that are sol- tubules are constructed in such a way that dermal laminae, the epidermal laminae of (which extends distally from its connec- The coronary cushion is the elastic por- involved in that institution’s Hoof Project. idly cemented together with keratin. One they resist compression of the hoof wall the wall, and the inter-laminar horn of the tion with the pastern bone or first pha- tion of the coronary band. It is a fibro-fatty Information from these researchers comes of its tasks is to protect the hoof wall when the horse’s foot bears weight. white line. Fourth is the sole corium, which lanx (P1); the coffin bone, also known as cushion that is thickest in the center and from past interviews and papers they have from drying out. The hoof wall should be Beneath the surface of the coronet is the is composed of fine hair-like papillae over the third phalanx (P3) or distal phalanx thinnest at the quarters where it attaches authored. Other infor- the entire inner surface of the sole. These (which extends distally from the short to the lateral cartilage. It then widens out mation comes from a internal foot S truC tureS papillae furnish nourishment and growth pastern bone); and the navicular bone, and thickens to form the base of the bulbs variety of papers and LAMiNAE THE CORONET to the sole. Fifth is the frog corium, which also known as the distal sesamoid bone, of the heel, where it blends in with the digi- textbooks. skin/dermis is similar in structure to the sole corium located behind and distal to the short tal cushion. The coronary cushion helps in laminar corium (corim of the skin) It should be noted secondary connective tissue and furnishes nourishment and growth to pastern bone and behind and proxi- the reduction and transfer of compression lamellae that hoof and foot are skin/epidermis the frog. mal to the coffin bone. The bones of the between the hoof wall and the coffin bone not synonymous. The extensor tendon Back to the parts of the foot that are foot and leg are connected by joints and as well as other internal foot parts. perioplic corium hoof or hoof wall, gen- primary readily visible. On the solar surface is the ligaments, so an injury to one can have a The inner foot is serviced by a blood sup- erally speaking, is the lamellae periople sole. The structure of the sole is similar to negative effect on the others. ply that is pumped by the heart through P2 three-layered outer coronary corium that of the wall, with tubules running verti- the arteries to the foot and is assisted in its surface of the foot. coronary band cally as formed by the papillae of the sole Soft Tissues return to the heart by a pumping mecha- The foot, on the other stratum corium. These tubules curl near the ground There are two key tendons within the nism within the foot facilitated by com- hand, includes the lamellae coffin germinativum P3 surface, which accounts for the self-limit- foot. The extensor tendon attaches to the pression involving a complex network of (stratum bone—P3 of coronary band hoof and all the bones, lamellatum) ing growth of the sole and causes shedding. front of the coffin bone and the deep digital veins whenever the horse bears weight blood vessels, liga- hoof wall The sole is not designed to constantly bear flexor tendon attaches to the bottom of the on the foot. They lymphatic system of the ments, tendons, and (stratum weight from the ground surface, but it is coffin bone. limbs also requires this pumping action to tectorium) nerves therein. hoof wall designed to bear internal weight. The navicular bursa is positioned be- move fluids. This is one reason that a horse (stratum medium) hoof wall An integral part of the foot is the frog, tween the deep digital flexor tendon and standing still for a long time will “stock (stratum The Outer Hoof medium) a wedge-shaped mass that occupies angles the flexor surface of the navicular bone and up” because fluids in the legs are not being We begin with that bounded by the bars and the sole. The frog helps reduce concussion on the bone. An- pumped back up the limbs by cycles of foot rather innocuous-ap- lamellae is divided into the apex, which is the for- other inner foot structure that helps absorb loading and unloading. (stratum lamellatum) laminar pearing exterior hoof corium ward-most point; the base, which is the concussion is the digital cushion located hoof wall wall. It plays a com- (stratum tectorium) rear portion; and the frog stay, which is the between the distal coffin bone and the Take-Home Message plicated role to house central ridge. The frog is about 50% water sole. The digital cushion is a wedge-shaped Because the foot plays such a key role in and protect the sensi- and is quite soft. structure with a fibro-fatty composition. It the horse’s ability to survive and function, tive inner foot, support The frog serves as a shock absorber in is very elastic and has very few blood ves- we will end this dissertation on the anat- weight, resist wear, conduct moisture, and approximately 25% water. coronary band. It is the primary growth two ways. First, it helps absorb concus- sels or nerves. When the digital cushion is omy of the foot with the oldest of clichés: absorb shock. The middle layer of the hoof wall com- and nutritional source for the hoof wall. sive force from the ground and, second, compressed by the pastern bones and frog “No foot, no horse.” H In order to accomplish these tasks, the prises the bulk of the wall and is the dens- Within this structure lies a massive supply it acts as a stop that redirects concussive with weight bearing, it absorbs shock, cush- hoof wall and the foot must be healthy. It est portion. The inner layer is the laminar of blood vessels that feed the hoof. These force coming down from the bony column ions the bones, and is divided by the frog’s About the Author is at this point that the owner or caretaker layer. It is concave from side to side and blood vessels, combined with nerves, form through the lateral cartilages and the hoof. exterior spine so that it is forced outward Les Sellnow is a free-lance writer based near Riverton, plays a role. Because we have the horse in bears a multitude of primary and second- a sensitive layer that is attached to the in- The heels of the hoof form the most cau- and obliquely upward against the lateral Wyo. He specializes in articles on equine research, and he an environment of our choosing, the natural ary leaf-like laminae, which attach the cof- side of the hoof wall and the third phalanx dal part of the bearing surface of the hoof cartilages. The lateral cartilages are part operates a ranch where he raises horses and livestock. He selection process does not come into play. fin bone to the inside of the hoof wall, simi- (coffin bone). wall. There the wall makes an acute change fibrous tissue and part hyaline cartilage. has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the In the wild, a horse with poor feet didn’t lar to Velcro. There are some 600 primary Injury to the coronary band can have a in direction, turning back toward the toe. They slope upward and backward from the young Horse, and the Journey of the western Horse, survive and its genes were not passed on. laminae, each of which bears 100 or more serious negative effect on hoof growth and The portions that turn toward the toe are wings of the coffin bone and reach above published by Eclipse Press and available at www.Exclusively Not so today. Some horses with horrid feet secondary laminae on its surface. These development. If the injury to the coronary the bars of the foot. the margin of the coronary band. Equine.com or by calling 800/582-5604.

24 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 25 SUCCEED® DIGESTIVE HEALTH PERFORMANCE SERIES “ I assumed my gelding was just anatomy—the naturally volatile and diffi cult. But now I know better.” head and neck How digestive health can affect a horse’s attitude and temperament. By Les seLLnow he equine head can be compared to a computer. Housed within the skull are the major “components—the brain and No matter the conformation of your Though only 26 years old, Kate Levy Tthe sense organs. In addition to functioning like a computer, is already a veteran rider in the show the equine head contains teeth for cropping grass and chewing chosen breed, the heads and necks of jumping arena. She’s competed at the food, and all of the necessary components for moving the food to Grand Prix level since she was 18, while the digestive system, as well as housing the respiratory apparatus horses serve many purposes completing her International Business that allows for air to be in- degree at Georgetown University. spired and expired. In 2003 Kate obtained a gray Belgian Connecting the neck, which also serves as an important element of balance as Warmblood gelding as part of a multiple head to the rest of well as containing vertebrae and a continuation of tubes for the horse deal. “Vent du Nord was thrown the body is the movement of food, water, air, and blood. in at the end,” she recalls. “But I didn’t The shape of a horse’s head and neck is often the focal point of really want him. He was so ornery and discussion when equine beauty is the topic. To the Arabian horse stubborn.” fancier, the broad forehead, dished face, ears that tip in, and a Kate had seen diffi cult horses before. tiny muzzle are all attractive components when perched “Top performance horses typically have Jumper rider Kate Levy learned that digestive health can help, or on an arched neck. The draft horse fancier likely lots of character and eccentricities. But hinder, a horse’s attitude and performance. could care less for a head that appears to Vent du Nord was something else. At fi rst have been sculpted. To that indi- I swear I spent more time on the ground Since then, Kate has been reaping the Horses’ digestive tracts maintain vidual a large head that is than I did on his back. He would spin and benefi ts. “Vent du Nord’s temperament a delicate balance that can easily be proportionate with rear. And it was hard to get him in form.” has really improved. Now he approaches altered by the challenges of performance a large “Everyone I knew suggested I should his work seriously, and he’s less excitable management and care. SUCCEED is get rid of him. But while I value their and unruly. He’s becoming more and a unique, daily nutrient program that advice, I could tell Vent du Nord had more of a show horse.” supports complete digestive health under potential. Maybe I was naïve, but I refused The value of optimal digestive health these rigorous conditions. to give up.” was apparent in other ways too. “SUCCEED “Vent du Nord still has his bad days, In 2005 the gelding was showing has helped his physical condition too. The believe me. But he’s consistently better. obvious signs of digestive imbalance. “He horse was always thin, with a slight build. And the results speak for themselves. had chronic diarrhea,” Kate says. “We He had a good appetite and ate fi ne, but I use SUCCEED on every horse now. It’s tried everything. All those products, all the feed seemed to just go right through an essential part of my program.” that money… and nothing worked.” him. Now he’s gained weight, and kept That’s when she decided to try it on. He’s more fi t, with a more athletic SUCCEED® Digestive Conditioning build. Even his form is better.” Program®. “I’d read about SUCCEED. Ultimately, the benefi ts were evident I knew International Grand Prix jumper in the show ring too. “Vent du Nord is Laura Kraut was using SUCCEED on nine now, and he’s placed in three World all her horses. So I tried it. And it really Cup Grand Prix classes. Three years ago worked wonders. The problem went away it was a miracle to even get through the for good. in-gate of the show ring, let alone actually But the benefi ts of SUCCEED went fi nish a jumper class in his saddle.” www.SucceedDCP.com beyond solving Kate’s initial problem. Kate now appreciates the impact “What really got my attention were the that a horse’s digestive health can have Available from select tack and feed stores, changes in Vent du Nord’s attitude. It was on its appearance, temperament and or ask your veterinarian. like night and day. Not all at once, but performance. “I feel like we have an

To locate a dealer or for more information, editor’s Note ustration

gradually I got to see more of the horse advantage, just knowing what SUCCEED call toll-free 866-270-7939. This is the sixth in a 12-part series of articles on equine iLL I hoped was hiding in there somewhere.” can do.” anatomy and physiology. Future topics include the hoof, the head and neck, the back, muscles, tendons and ligaments, the digestive system, the circulatory and respiratory in Peterson B

systems, and the reproductive system. o r

Photos © 2007, Anne Gittins SUCCEED® and Digestive Conditioning Program® are registered trademarks of Freedom Health, LLC. ©2007. All Rights Reserved. PATENT PENDING. December 2006 The horse www.TheHorse.com 27

Succeed_Levy_1569.indd 1 2/7/07 10:27:45 AM SUCCEED® DIGESTIVE HEALTH PERFORMANCE SERIES “ I assumed my gelding was just anatomy—the naturally volatile and diffi cult. But now I know better.” head and neck How digestive health can affect a horse’s attitude and temperament. By Les seLLnow he equine head can be compared to a computer. Housed within the skull are the major “components—the brain and No matter the conformation of your Though only 26 years old, Kate Levy Tthe sense organs. In addition to functioning like a computer, is already a veteran rider in the show the equine head contains teeth for cropping grass and chewing chosen breed, the heads and necks of jumping arena. She’s competed at the food, and all of the necessary components for moving the food to Grand Prix level since she was 18, while the digestive system, as well as housing the respiratory apparatus horses serve many purposes completing her International Business that allows for air to be in- degree at Georgetown University. spired and expired. In 2003 Kate obtained a gray Belgian Connecting the neck, which also serves as an important element of balance as Warmblood gelding as part of a multiple head to the rest of well as containing vertebrae and a continuation of tubes for the horse deal. “Vent du Nord was thrown the body is the movement of food, water, air, and blood. in at the end,” she recalls. “But I didn’t The shape of a horse’s head and neck is often the focal point of really want him. He was so ornery and discussion when equine beauty is the topic. To the Arabian horse stubborn.” fancier, the broad forehead, dished face, ears that tip in, and a Kate had seen diffi cult horses before. tiny muzzle are all attractive components when perched “Top performance horses typically have Jumper rider Kate Levy learned that digestive health can help, or on an arched neck. The draft horse fancier likely lots of character and eccentricities. But hinder, a horse’s attitude and performance. could care less for a head that appears to Vent du Nord was something else. At fi rst have been sculpted. To that indi- I swear I spent more time on the ground Since then, Kate has been reaping the Horses’ digestive tracts maintain vidual a large head that is than I did on his back. He would spin and benefi ts. “Vent du Nord’s temperament a delicate balance that can easily be proportionate with rear. And it was hard to get him in form.” has really improved. Now he approaches altered by the challenges of performance a large “Everyone I knew suggested I should his work seriously, and he’s less excitable management and care. SUCCEED is get rid of him. But while I value their and unruly. He’s becoming more and a unique, daily nutrient program that advice, I could tell Vent du Nord had more of a show horse.” supports complete digestive health under potential. Maybe I was naïve, but I refused The value of optimal digestive health these rigorous conditions. to give up.” was apparent in other ways too. “SUCCEED “Vent du Nord still has his bad days, In 2005 the gelding was showing has helped his physical condition too. The believe me. But he’s consistently better. obvious signs of digestive imbalance. “He horse was always thin, with a slight build. And the results speak for themselves. had chronic diarrhea,” Kate says. “We He had a good appetite and ate fi ne, but I use SUCCEED on every horse now. It’s tried everything. All those products, all the feed seemed to just go right through an essential part of my program.” that money… and nothing worked.” him. Now he’s gained weight, and kept That’s when she decided to try it on. He’s more fi t, with a more athletic SUCCEED® Digestive Conditioning build. Even his form is better.” Program®. “I’d read about SUCCEED. Ultimately, the benefi ts were evident I knew International Grand Prix jumper in the show ring too. “Vent du Nord is Laura Kraut was using SUCCEED on nine now, and he’s placed in three World all her horses. So I tried it. And it really Cup Grand Prix classes. Three years ago worked wonders. The problem went away it was a miracle to even get through the for good. in-gate of the show ring, let alone actually But the benefi ts of SUCCEED went fi nish a jumper class in his saddle.” www.SucceedDCP.com beyond solving Kate’s initial problem. Kate now appreciates the impact “What really got my attention were the that a horse’s digestive health can have Available from select tack and feed stores, changes in Vent du Nord’s attitude. It was on its appearance, temperament and or ask your veterinarian. like night and day. Not all at once, but performance. “I feel like we have an

To locate a dealer or for more information, editor’s Note ustration gradually I got to see more of the horse advantage, just knowing what SUCCEED call toll-free 866-270-7939. This is the sixth in a 12-part series of articles on equine iLL I hoped was hiding in there somewhere.” can do.” anatomy and physiology. Future topics include the hoof, the head and neck, the back, muscles, tendons and ligaments, the digestive system, the circulatory and respiratory in Peterson B

systems, and the reproductive system. o r

Succeed_Levy_1569.indd 1 2/7/07 10:27:45 AM immovable joints where the bones are leads directly into the nasophaynx. The food and water head down head and neC k nasal opening. bound by fibrous tissue that ossifies as the pharynx is a passageway, comprised of the esophagus and into the A horse’s hearing is more horse matures. muscle and membranous tissue, that is lo- stomach instead of winding acute than that of a human as guttural pouches The equine brain is located within a cra- cated between the mouth-nostrils area and up in the trachea and the its uniquely shaped ears funnel nial cavity. The cranial cavity is partially the larynx and esophagus. The portion of lungs. brain sounds to the brain. In a Sep- divided by a down-growth of the skull the pharynx above the level of the soft pal- The horse’s tongue lies on base of ears tember 2005 article in The Horse roof, with the rostral compartment hous- ate is the nasopharynx. the floor of the mouth and is (www.TheHorse.com/emag. auditory ing the cerebral hemispheres of the fore- The larynx is the upper end of the tra- composed of a mass of muscle canal aspx?id=6016), the writer noted brain and the caudal compartment hous- chea or windpipe. It is a tubular structure anchored by the hyoid bone that horses’ ears are finely tuned nerves body and a neck that is muscular and ing the cerebellum of the rear brain. The comprised of muscle and cartilage that and the bodies of the left and instruments designed to convert strong are the components being sought. brain is continuous with the spinal cord. contains the vocal cords and connects right mandibles—lower jaw. internal carotid sound waves in the environ- artery An anatomically correct horse will have The brain lies in the upper forehead of the the nasopharynx with the trachea. The nerves ment into action potentials in a head that is proportionate to its body horse and, of course, is the key component trachea is a cartilaginous and membra- Something To Chew On the auditory nerve. This nerve, size, and the shape will be characteristic of in this unique “computer.” nous tube descending from the larynx and One of the skull’s most im- glottis common carotid which is located at the base of the breed. branching into the right and portant components involves artery the skull, sends information to There are a couple of t he e ar left bronchi. the teeth. They are used for the brain to be translated and other requirements when The roof of the mouth is cropping grass and grinding ustration interpreted. iLL looking at the ideal equine formed from the hard palate food as part of the masticating external carotid artery The horse uses his pinna (the head. The forehead should in front and the soft palate process. When a foal is born, large, cup-like part of the ear close behind and continuous that you can see) to collect sound be broad and well defined incus it is generally toothless, but in Peterson B

malleus o to provide space for wide- with it. very soon it will have a full set r waves from the environment. set eyes. The lower jaw stapes In technical terms, with an of baby teeth (24). They are Dr. Made of cartilage, the pinna can should also be well de- assist from the above-men- divided into six upper and six rotate to capture sound waves fined and with good width tioned authors, here is how lower incisors and six upper and six lower believing that it was best left in the hands from all directions because horses have 16 between the branches so the apparatus functions: molars, and they are replaced with adult of nature. That is no longer case in much auricular muscles controlling their pinna. that there is ample space When the horse is breath- teeth around age three. of the equine world today, and modern-day After being trapped by the pinna, the col- for the larynx. In addition, ing, the free edge of the soft The adult male horse has six upper and horses are healthier because of it. lected sound waves are funneled through the nostrils should be wide palate is usually under the six lower incisors; six upper and six lower the external ear canal (commonly referred cochlea and capable of flaring into epiglottis and the laryngeal pre-molars (the most forward set of cheek The Better to See and Hear You... to as the auditory canal) to the middle ear even larger openings so the drum entrance is open. During teeth); six upper and six lower molars (the There are some aspects of equine ear, where they cause the eardrum, a thin horse can increase air in- swallowing, muscles raise cheek teeth at the rear of the mouth); two anatomy that have similarities to human membrane, to vibrate. take during exercise. (While the tongue, pressing food or upper and two lower canine teeth; and anatomy; the eye is not one of them. The These vibrations are sent through the that point is widely held by water against the hard pal- two wolf teeth located adjacent to the most basic difference stems from the fact ossicles, a series of three tiny bones called many horse owners, there ate. The root of the tongue is premolars in the horse’s upper jaw. that humans are predators and horses are the malleus, incus, and stapes. Finally, they are those in the scientific ustration pulled rearward, the laryngeal The incisors are used for cropping prey animals. Thus, the eyes of humans are reach the inner ear, where they cause vi- community who say there iLL entrance is narrowed, and grass and the molars for grinding it in close together and can focus quickly on ob- brations in a snail-shaped structure called is little or no research data the soft palate is elevated to preparation for the digestive process. Aid- jects both near and far. Looking at objects the cochlea. to support the contention the caudal wall of the phar- ing the cause are salivary glands that, in to right or left involves turning the head in Running up and down the cochlea are that flaring nostrils permit in Peterson ynx. Increased pressure in the the adult horse, can produce as much as that direction. Human eyes are more com- extremely sensitive hair cells that act as B o additional intake of air.) r pharynx forces feed or water 10 gallons of saliva per day. parable to the eyes of cats and dogs than transducers. When these hair cells bend, r.

As we explore the anato- D into the esophagus where in- Adult females normally have the same horses. they generate electrical signals that stimu- my of the equine head and voluntary contractions cause complement of teeth as the males, minus As a prey animal, the horse has de- late the auditory nerve. This nerve passes neck, it must be pointed out that the infor- The respiratory tract starts with the nos- it to journey on to the stomach. the canine teeth. veloped both monocular mation in this article comes from a wide trils, which are the openings into the nasal What this all means in simple terms The tooth of the horse is described as be- and binocular vision. This the eye variety of sources, including textbooks and cavity. The perpendicular partition sepa- is that during the breathing process, the ing hypsodont. Simply put, this means the means that the horse can papers on equine anatomy. However, spe- rating the nasal cavity into left and right pharynx and soft palate form a smooth, teeth are constantly erupting as the grind- see an image with both Orbicularis oculi muscle cial attribution must once again be given to halves is known as the median nasal sep- uninterrupted passageway for the flow of ing action of eating wears away the crown eyes—binocular—or with retina Tarsal plate The Coloring Atlas Of The Horse, authored tum. It is composed of bony, cartilaginous, air into the trachea. When the horse swal- surface. One can compare it to chalk be- one eye only—monocular. tapetum by former Colorado State University fac- and membranous parts. lows, the pharynx and soft palate move so ing used on a blackboard. After a time, the Humans have binocular vi- Meibomian ulty members Thomas O. McCracken, MS, Structures within the nasal cavity in- that food is directed into the esophagus chalk becomes so short as to be worthless. sion only. With monocular gland and Robert A. Kainer, DVM, MS. clude the turbinate bones, also known rather than the trachea. There can be a va- It is basically the same with the horse’s vision, the brain often is re- Cilium or as nasal conchae. They contain mucous- riety of afflictions capable of altering the teeth. ceiving different messages eyelash secreting epithelium that functions as soft palate, causing caudal displacement Perhaps one of the most improved areas from each of its eyes. vitreous Bone Head, With Lots of Air chamber optic lens nerve It might come as a surprise to some something of an air conditioning pro- and preventing its return to the normal of equine health care involves dental pro- Important to the good pupil horse owners to realize the equine skull is cess as it warms, moisturizes, and filters breathing position. cedures. Research has shown when teeth health of equine eyes are the optic disc comprised of 34 bones, most of them flat. inspired air. The nasal conchae and the Lending a major assist in preventing are properly cared for, it allows the horse lacrimal glands located just iris ustration iLL During the birthing process, these median nasal septum divide the nasal cav- food from being inspired into the lungs to masticate its food better and, as a result, above the eye. Tears secret- cornea bones yield and overlap, allowing the skull ity into passageways; each passageway is is the epiglottis, a lid-like structure over- make better use of the nutrients being in- ed by the lacrimal glands

to be somewhat compressed and thus al- called a meatus. hanging the entrance to the larynx. Its job gested. wash over the eye and make ciliary body in Peterson B o lowing for easier parturition. The bones The largest of these passageways is is to close the laryngeal opening when the In the past, many horse owners paid their way downward, ulti- sclera r have fibrous joints, which are basically known as the ventral nasal meatus and horse swallows, thus making certain that little attention to their horses’ teeth, mately exiting through the Dr.

28 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 29 immovable joints where the bones are leads directly into the nasophaynx. The food and water head down head and neC k nasal opening. bound by fibrous tissue that ossifies as the pharynx is a passageway, comprised of the esophagus and into the A horse’s hearing is more horse matures. muscle and membranous tissue, that is lo- stomach instead of winding acute than that of a human as guttural pouches The equine brain is located within a cra- cated between the mouth-nostrils area and up in the trachea and the its uniquely shaped ears funnel nial cavity. The cranial cavity is partially the larynx and esophagus. The portion of lungs. brain sounds to the brain. In a Sep- divided by a down-growth of the skull the pharynx above the level of the soft pal- The horse’s tongue lies on base of ears tember 2005 article in The Horse roof, with the rostral compartment hous- ate is the nasopharynx. the floor of the mouth and is (www.TheHorse.com/emag. auditory ing the cerebral hemispheres of the fore- The larynx is the upper end of the tra- composed of a mass of muscle canal aspx?id=6016), the writer noted brain and the caudal compartment hous- chea or windpipe. It is a tubular structure anchored by the hyoid bone that horses’ ears are finely tuned nerves body and a neck that is muscular and ing the cerebellum of the rear brain. The comprised of muscle and cartilage that and the bodies of the left and instruments designed to convert strong are the components being sought. brain is continuous with the spinal cord. contains the vocal cords and connects right mandibles—lower jaw. internal carotid sound waves in the environ- artery An anatomically correct horse will have The brain lies in the upper forehead of the the nasopharynx with the trachea. The nerves ment into action potentials in a head that is proportionate to its body horse and, of course, is the key component trachea is a cartilaginous and membra- Something To Chew On the auditory nerve. This nerve, size, and the shape will be characteristic of in this unique “computer.” nous tube descending from the larynx and One of the skull’s most im- glottis common carotid which is located at the base of the breed. branching into the right and portant components involves artery the skull, sends information to There are a couple of t he e ar left bronchi. the teeth. They are used for the brain to be translated and other requirements when The roof of the mouth is cropping grass and grinding ustration interpreted. iLL looking at the ideal equine formed from the hard palate food as part of the masticating external carotid artery The horse uses his pinna (the head. The forehead should in front and the soft palate process. When a foal is born, large, cup-like part of the ear close behind and continuous that you can see) to collect sound be broad and well defined incus it is generally toothless, but in Peterson B

28 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 29 tention to a component that is unique to with air, as is the case with an inflated bal- the horse—guttural pouches. There is a loon. guttural pouch on either side of the horse’s Why nature provided equids—and no the head, and each is divided into a larger in- other mammals—with guttural pouches ner and small outer compartment. The is a mystery, with some scientists thinking guttural pouch is a grapefruit-sized sac the pouches might have something to do By Les seLLnowequine back that is interposed in the eustachian tube with balance. One thing is certain, when that connects the middle ear with the na- there is a fungal attack in the guttural sal passage. pouch, it can be a serious health problem. orses have been carrying burdens on their backs since man discovered that he editor’s Note the impulses to the brain. The normal guttural pouch can be de- could cover more ground faster while riding a horse as opposed to striding along This is the seventh in a 12-part series of articles on equine scribed as an air-filled sac. However, while Along the Neck on his own two legs. Man also discovered that it was far less strenuous to pack a anatomy and physiology. Future topics include muscles, H tendons and ligaments, the digestive system, the circula- A Pouch for Trouble the image of a balloon comes to mind, the As mentioned earlier, the shape of load on a horse’s back rather than on his own. tory and respiratory systems, and the reproductive system. Before leaving the skull, we must call at- normal guttural pouch is not distended a horse’s neck can be involved in what As use of the horse increased, so did problems with the equine back. Some of them Previous articles can be found on www.TheHorse.com. one considers attractive or unattract- are the result of conformation. It takes a strong, well-conformed back to handle the ive conformation, but that sometimes rigors of trail riding, performing, and packing. Other problems have been man-made. has little to do with function. A short, Even a horse with excellent conformation can wind up with back problems if ridden cresty neck is undesirable because it can by a rider out of balance or if outfitted with inappropriate tack. inhibit proper function. If the thickness In this article, we’ll take a look at the equine back—how it is structured, extends all the way into the throatlatch, proper conformation, and some of the problems than can afflict it. it can cause problems. Both the trachea As usual, there are many sources, but we will draw heavi- and the esophagus enter the neck at that ly on two individuals who have authored papers and point—as do a vital network of veins and presided over discussions on the equine back. arteries that convey the blood supply to and One is Kevin Haussler, DVM, DC, PhD, Subtle problems in the from the brain. When a horse with a thick a licensed veterinary chiroprac- throatlatch is asked to “set its head” or car- tor who teaches at back—and elsewhere ry its head in a perpendicular frame, these vital passageways often are constricted. that affect the back—can A short, heavy neck also restricts the use of the neck and head as balancing mecha- create lameness or nisms. disability in the One of the methods utilized in determining optimum neck conformation is to performance or riding measure the top and bottom of the neck. The top runs from the poll to the withers, horse and the bottom runs from the throatlatch to the neck-shoulder junction. The proper ratio in the minds of many is two to one, top to bottom. There are seven cervical vertebrae in the horse’s neck, with the spinal cord exiting the brain and running through them. The vertebrae are connected via cartilaginous joints. These joints are slightly movable and are united by connective tissue. Prob- lems that develop within, or to, the cervical vertebrae can mean serious problems. There is a correlation between the length of the cervical vertebrae and the length of the neck—the longer the individual vertebrae, the longer the neck. The vertebrae of the neck connect with the vertebral column of the back, which we will be discussing next month. h About the Author s Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he

operates a ranch where he raises horses and livestock. He ustration has authored several fiction and non-fiction books, includ- iLL ing understanding equine Lameness, understanding the young Horse, and the Journey of the western Horse, published by Eclipse Press and available at www.Exclusively in Peterson B

Equine.com or by calling 800/582-5604. o r

30 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 31 tention to a component that is unique to with air, as is the case with an inflated bal- the horse—guttural pouches. There is a loon. guttural pouch on either side of the horse’s Why nature provided equids—and no the head, and each is divided into a larger in- other mammals—with guttural pouches ner and small outer compartment. The is a mystery, with some scientists thinking guttural pouch is a grapefruit-sized sac the pouches might have something to do By Les seLLnowequine back that is interposed in the eustachian tube with balance. One thing is certain, when that connects the middle ear with the na- there is a fungal attack in the guttural sal passage. pouch, it can be a serious health problem. orses have been carrying burdens on their backs since man discovered that he editor’s Note the impulses to the brain. The normal guttural pouch can be de- could cover more ground faster while riding a horse as opposed to striding along This is the seventh in a 12-part series of articles on equine scribed as an air-filled sac. However, while Along the Neck on his own two legs. Man also discovered that it was far less strenuous to pack a anatomy and physiology. Future topics include muscles, H tendons and ligaments, the digestive system, the circula- A Pouch for Trouble the image of a balloon comes to mind, the As mentioned earlier, the shape of load on a horse’s back rather than on his own. tory and respiratory systems, and the reproductive system. Before leaving the skull, we must call at- normal guttural pouch is not distended a horse’s neck can be involved in what As use of the horse increased, so did problems with the equine back. Some of them Previous articles can be found on www.TheHorse.com. one considers attractive or unattract- are the result of conformation. It takes a strong, well-conformed back to handle the ive conformation, but that sometimes rigors of trail riding, performing, and packing. Other problems have been man-made. has little to do with function. A short, Even a horse with excellent conformation can wind up with back problems if ridden cresty neck is undesirable because it can by a rider out of balance or if outfitted with inappropriate tack. inhibit proper function. If the thickness In this article, we’ll take a look at the equine back—how it is structured, extends all the way into the throatlatch, proper conformation, and some of the problems than can afflict it. it can cause problems. Both the trachea As usual, there are many sources, but we will draw heavi- and the esophagus enter the neck at that ly on two individuals who have authored papers and point—as do a vital network of veins and presided over discussions on the equine back. arteries that convey the blood supply to and One is Kevin Haussler, DVM, DC, PhD, Subtle problems in the from the brain. When a horse with a thick a licensed veterinary chiroprac- throatlatch is asked to “set its head” or car- tor who teaches at back—and elsewhere ry its head in a perpendicular frame, these vital passageways often are constricted. that affect the back—can A short, heavy neck also restricts the use of the neck and head as balancing mecha- create lameness or nisms. disability in the One of the methods utilized in determining optimum neck conformation is to performance or riding measure the top and bottom of the neck. The top runs from the poll to the withers, horse and the bottom runs from the throatlatch to the neck-shoulder junction. The proper ratio in the minds of many is two to one, top to bottom. There are seven cervical vertebrae in the horse’s neck, with the spinal cord exiting the brain and running through them. The vertebrae are connected via cartilaginous joints. These joints are slightly movable and are united by connective tissue. Prob- lems that develop within, or to, the cervical vertebrae can mean serious problems. There is a correlation between the length of the cervical vertebrae and the length of the neck—the longer the individual vertebrae, the longer the neck. The vertebrae of the neck connect with the vertebral column of the back, which we will be discussing next month. h About the Author s Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he

Equine.com or by calling 800/582-5604. o r

30 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 31 a particular reason. The processes or pro- A significant characteristic of the spine suffering from lordosis. This, too, is a con- The relative rigid- jections provide the site for attachment of is its rigidity. There is some movement dition that will cause a saddle to fit poorly ity of the back pro- muscles that support the head, neck and from side to side and up and down along and can be the source of soreness and a vides the strength front legs. In like manner, the vertebrae of the back, but not a great deal. wide variety of other back problems. needed to support a sacral lumbar thoracic cervical the sacral area help support the hind legs In contrast, the vertebrae in the neck When viewed from the side, the rider’s weight. How- coccygeal and the vertebral ligaments form broad at- and in the tail are much more flexible, al- topline—the distance between the withers ever, there are disci- tachments to the bones and muscles of the lowing the horse to raise and lower its head and croup—should be less than the dis- plines where at least pelvis. and move it from side to side. The flex- tance between front and rear legs along the some movement at ibility of the tail provides the horse with a belly, or underline. If the topline is longer, the vertebral joints Cornell University’s School of Veterinary The Vertebrae strong weapon against attacking insects. it is an indication that the horse’s back is in the thoracic and Medicine. Information from Haussler Now, with Haussler’s help, along with The amount and direction of flexibility is too long and that it will be weak and lack- lumbar areas is re- stems from interviews and presentations textbook information, we’ll take a look at determined mostly by joint size and ing in balance. There should be a slight dip quired. at AAEP conventions. the individual bones in the spine. shape. behind the withers where the saddle rests Perhaps the The other source is Doyle Meadows, The typical vertebra consists of a ver- The joints that connect the vertebrae are and a gentle sweep upward over the loins discipline that re- PhD, a professor in the Animal Science tebral body (the main bulk of the bone) known as cartilaginous joints. These are and point of croup. quires the great- Department at the University of A key part of back conformation is the est range of spinal Tennessee. One of Doyle’s pa- loin—the area between the last rib and the movement and pers on equine conformation croup. The loin should be well-muscled, strength is dressage. was included in the Horse Indus- strong, and relatively short so that it can Jumping high fences try Handbook published by the convey power from the rear legs forward. also requires move- American Youth Horse Council. The croup is the area that extends from ment in the form of The horse’s spinal column starts at the poll and goes to the end of the In addition, we will draw on in- the loins to the tailhead. It should be long rotation of the back tail (see areas defined above). formation included in anatomy and gently sloping, with the amount of and hind limbs. textbooks. slope varying from breed to breed and One of the prime responsibilities of the largements. The key component in a horse’s horse to horse. A long croup enables a vertebral column is to protect the spinal When we consider that we are dealing back is his spine. It begins at the horse to have a long stride as well as pro- cord that runs through it and the complex with an area of equine anatomy with rela-

head and travels along the neck, 1 2 Courtesy Dr. Jean-Marie Denoix viding a setting for proper dimension and nerve system that branches from the spinal tively small joints with little movement, it withers, back, loin, and croup, Medial cross sections of the spine at the lumbosacral junction. Normal anatomy is shown in image 1; anky- solid muscling in the hindquarters. cord at intervals all along the spine. As the becomes apparent that there is potential and it ends in the tail. How this losis and degeneration of L6 is shown in image 2. nerve structure exits the spine, the nerves for performance-limiting injuries if some- spinal column is conformed can Strength and Flexibility divide into various branches that fan out thing happens to damage this relatively have a great deal to do with the Strong muscles are needed to support within the horse’s body and go to the joints, rigid structure. horse staying sound, healthy, and free of and several vertebral or spinal processes joints that are slightly movable or immov- the back. They are divided into two catego- muscles, internal organs, and skin. back pain even when involved in arduous (smaller wings projecting off the vertebral able, depending on the bones involved. ries—superficial and deep. Nerve impulses travel from the brain Helping Injuries pursuits. body). The length of an individual vertebra Cartilaginous joints are united by fibro- The large, superficial back muscles span and spinal cord and out of the spinal In the past, when a back injury was sus- can vary from one horse to another. cartilage, hyaline cartilage, or both. The large regions of the spine and ensure co- nerves to all parts of the body. Similarly, pected, about the only therapy utilized was Anatomy of the Spine There is a strong correlation between connective tissue between two vertebrae is ordinated back movements. Smaller, deep nerve impulses travel back to the brain rest. In more recent years, however, new Generally speaking, the horse has 54 ver- vertebral length and the length of various comprised of both types of cartilage. Car- back muscles connect one or two vertebrae via the peripheral nerves and spinal cord. weapons have been added to a veterinar- tebrae in this spinal or vertebral column component parts. For example, a horse tilage and soft tissue form discs between and act to move or stabilize each individual The horse’s overall nerve structure serves ians’ arsenal, including chiropractic and (vertebra is singular, vertebrae is plural). with long vertebrae will tend to have a long individual vertebrae to absorb the shock vertebra. as the message-carrying system between acupuncture. We say “generally speaking” because the neck, back, loin, croup, and tail. Again, and concussion produced by movement. the brain and all areas Back and neck injuries in the horse can number of vertebrae in a horse’s tail can more is not necessarily better. Yes, we of the body. Nerves also involve a variety of causes. Often the injury vary. Haussler tells us that there can be as want a horse to have a long neck, but no, Back Conformation can sense pain and joint stems from trauma, such as a fall or tip- few as 51 total vertebrae and as many as we don’t want it to be overly long and un- Now we turn to Meadows for assistance movement. Pain sen- ping over backward. Problems also can 57. Using 54 as our average total for this wieldy. The same is true of the other areas in describing proper equine back confor- sors are found in the stem from poor conformation, poor saddle discussion, we find that there are seven of equine anatomy involved—back, loin, mation. Once we have this picture in mind, bones, joints, muscles, fit, over-exertion, and lack of fitness. cervical or neck vertebrae; 18 dorsal or croup, and tail. it will be easier to understand form and ligaments, and blood Haussler provides us with three classifi- thoracic vertebrae; six lumbar or loin ver- When discussing the properly con- function of the back. vessels of the back. cations for spinal injuries: tebrae; five sacral or croup vertebrae; and formed horse, we noted that the highest When considering a properly conformed When joints or ■ Soft tissue injuries involving muscles, 18 coccygeal or tail vertebrae. point of the back is at the withers, with a horse, the withers will be the highest point muscles don’t function tendons, and ligaments. The vertebrae are identified by clinicians slight decline where the saddle rests, then of the back. A prominent withers ensures correctly or nerves are ■ Osseous injuries involving bones and and researchers by number from head to an upward sweep at the croup. This does that the saddle will stay in place without irritated, the message joints; and tail. For example, the first cervical vertebra not mean that the spine itself is much excessive cinching. The equine backbone, system falters. ■ Neurological injuries involving the ner- is identified as C1 and the last one is C7. higher or lower at any point along the overall, is arched slightly upward, thus The diameter of the vous system.

The thoracic vertebrae are prefaced by T back. Instead, the dorsal spinal process helping provide strength and durability. Courtesy Dr. Jean-Marie Denoix spinal cord is at its When dealing with chiropractic, one A cross section of the back shows the spine and soft tissues (mus- and a number. T1 is the first thoracic verte- on the vertebrae’s upper surfaces are in- However, it also is a case where more is greatest in the cervical term is heard with frequency: Sublux- cles, tendons, and ligaments) surrounding the spine. bra and is located at the point of the shoul- volved. These bony, finlike projections are not better. If the back is arched too much, and lumbar regions. ation. Technically, subluxation means a der where the thoracic column begins. The at their longest at the withers and at their the horse is said to be roach backed, a con- These are the areas partial dislocation of a joint. However, in thoracic vertebrae end where the last rib shortest under the saddle, then project up- dition that can be the source of soreness Spinal ligaments connect the individual where nerve roots for the plexuses (a net- chiropractic terminology, it describes the attaches to the vertebral column. ward a bit more in the hip area. The spine and a limitation of performance capability. vertebrae and provide joint support. In ad- work of nerves) supplying the nerves of loss of normal motion due to pain, muscle The thoracic vertebrae closer to the neck itself runs in pretty much a straight line all On the other hand, if the back sags mark- dition, the horse’s spinal column is held un- the limbs originate. These two areas are spasms, or joint stiffness. With sublux- have prominent dorsal spinal processes for along the back. edly, we say the horse is sway-backed or der tension by the horse’s belly muscles. referred to as the cervical and lumbar en- ation, the joint surfaces are almost, but not

32 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 33 a particular reason. The processes or pro- A significant characteristic of the spine suffering from lordosis. This, too, is a con- The relative rigid- jections provide the site for attachment of is its rigidity. There is some movement dition that will cause a saddle to fit poorly ity of the back pro- muscles that support the head, neck and from side to side and up and down along and can be the source of soreness and a vides the strength front legs. In like manner, the vertebrae of the back, but not a great deal. wide variety of other back problems. needed to support a sacral lumbar thoracic cervical the sacral area help support the hind legs In contrast, the vertebrae in the neck When viewed from the side, the rider’s weight. How- coccygeal and the vertebral ligaments form broad at- and in the tail are much more flexible, al- topline—the distance between the withers ever, there are disci- tachments to the bones and muscles of the lowing the horse to raise and lower its head and croup—should be less than the dis- plines where at least pelvis. and move it from side to side. The flex- tance between front and rear legs along the some movement at ibility of the tail provides the horse with a belly, or underline. If the topline is longer, the vertebral joints Cornell University’s School of Veterinary The Vertebrae strong weapon against attacking insects. it is an indication that the horse’s back is in the thoracic and Medicine. Information from Haussler Now, with Haussler’s help, along with The amount and direction of flexibility is too long and that it will be weak and lack- lumbar areas is re- stems from interviews and presentations textbook information, we’ll take a look at determined mostly by joint size and ing in balance. There should be a slight dip quired. at AAEP conventions. the individual bones in the spine. shape. behind the withers where the saddle rests Perhaps the The other source is Doyle Meadows, The typical vertebra consists of a ver- The joints that connect the vertebrae are and a gentle sweep upward over the loins discipline that re- PhD, a professor in the Animal Science tebral body (the main bulk of the bone) known as cartilaginous joints. These are and point of croup. quires the great- Department at the University of A key part of back conformation is the est range of spinal Tennessee. One of Doyle’s pa- loin—the area between the last rib and the movement and pers on equine conformation croup. The loin should be well-muscled, strength is dressage. was included in the Horse Indus- strong, and relatively short so that it can Jumping high fences try Handbook published by the convey power from the rear legs forward. also requires move- American Youth Horse Council. The croup is the area that extends from ment in the form of The horse’s spinal column starts at the poll and goes to the end of the In addition, we will draw on in- the loins to the tailhead. It should be long rotation of the back tail (see areas defined above). formation included in anatomy and gently sloping, with the amount of and hind limbs. textbooks. slope varying from breed to breed and One of the prime responsibilities of the largements. The key component in a horse’s horse to horse. A long croup enables a vertebral column is to protect the spinal When we consider that we are dealing back is his spine. It begins at the horse to have a long stride as well as pro- cord that runs through it and the complex with an area of equine anatomy with rela-

32 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 33 the pairs of vertebrae. problem. When that is the case, the back Sometimes a subluxation problem is problem won’t be alleviated, no matter solved naturally, such as a horse rolling, what treatment is used, until the primary bending, or stretching. At other times, cause is removed. however, the problem persists and calls for The chiropractic adjustment consists of treatment. In many cases, the treatment a short, sharp thrust with the hands to a protocol involves both a veterinarian and specific area of the back. The approach is a chiropractor working under the auspices designed to release muscle spasms, allevi- body builders: of the attending veterinarian. (Today, more ate pain, and return the joint to its normal quite, in the correct position. The joint still and more veterinarians are adding chiro- range of motion. func tions, but not as well, and might be practic credentials to their portfolio.) The Normally, there are few side effects after painful. There might also be an impinge- reason for the dual approach is that many chiropractic treatment, but a horse might ment of the spinal nerves that exit between back problems are secondary to a primary occasionally become stiff and sore after being treated, especially if there is a lot of muscles inflammation or bony pathology, such as acute or active arthritis. Other back problems, such as those involving the discs between each pair of By Les seLLnow vertebrae, often are much more complicated—as is the case with humans—and could uscles are one of the require a different approach. most important com- Mponents in the equine body. Without them, the horse would be unable to walk, chew food, digest it, or even The chiropractic swish his tail. Muscles com- adjustment con- prise the largest tissue mass in the horse’s body. There are various types of sists of a short, muscles performing a wide variety of duties, but ba- sharp thrust with sically they all function in the same general way—a period of contraction or shortening of muscle fibers, the hands to a spe- followed by a period of muscle relaxation or length- cific area of the ening of muscle fibers. back. A horse’s conformation and muscle types can determine Take-Home Message The equine back is a well-designed how well he can perform certain structure in the properly conformed horse. However, when poor conformation is in- tasks, but all horses are subject volved and/or inappropriate tack is used, serious problems can arise. h to muscle injury and disease

ing understanding equine Lameness, understanding the o periodic paralysis (HYPP) and tying-up. As has been the young Horse, and the Journey of the western Horse, r case throughout this series, we will draw on a wide variety Dr. published by Eclipse Press and available at www.Exclusively of sources, including textbooks. However, a couple of researchers deserve Equine.com or by calling 800/582-5604. specific mention. Much of the information concerning description of muscle further reading structure comes from a paper authored by Craig H. Wood, PhD, coordinator AAEP Convention 2005: “Treating Sore Backs Table of Distance Learning at the University of Kentucky, and published in the Topic,” www.TheHorse.com/emag.aspx?id=6537. Horse Industry Handbook. When we discuss HYPP, the work of Sharon “Fitting the Saddle to the Withers,” www.TheHorse. Spier, DVM, Dipl ACVIM, PhD, associate professor at the University of com/emag.aspx?id=5700. editor’s Note “Hunter’s Bump,” www.TheHorse.com/emag.aspx? California, Davis, becomes a source of information. No discussion on ty- This is the eighth in a 12-part series of articles on equine id=4649. anatomy and physiology. Future topics include the tendons ing-up should be conducted without drawing on the research of Stephanie “Understanding Back Pain,” www.TheHorse.com/ and ligaments, the digestive system, the circulatory and Valberg, DVM, PhD, professor of large animal medicine and director of the emag.aspx?id=3901. respiratory systems, and the reproductive system. Equine Center at the University of Minnesota.

34 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 35 the pairs of vertebrae. problem. When that is the case, the back Sometimes a subluxation problem is problem won’t be alleviated, no matter solved naturally, such as a horse rolling, what treatment is used, until the primary bending, or stretching. At other times, cause is removed. however, the problem persists and calls for The chiropractic adjustment consists of treatment. In many cases, the treatment a short, sharp thrust with the hands to a protocol involves both a veterinarian and specific area of the back. The approach is a chiropractor working under the auspices designed to release muscle spasms, allevi- body builders: of the attending veterinarian. (Today, more ate pain, and return the joint to its normal quite, in the correct position. The joint still and more veterinarians are adding chiro- range of motion. func tions, but not as well, and might be practic credentials to their portfolio.) The Normally, there are few side effects after painful. There might also be an impinge- reason for the dual approach is that many chiropractic treatment, but a horse might ment of the spinal nerves that exit between back problems are secondary to a primary occasionally become stiff and sore after being treated, especially if there is a lot of muscles inflammation or bony pathology, such as acute or active arthritis. Other back problems, such as those involving the discs between each pair of By Les seLLnow vertebrae, often are much more complicated—as is the case with humans—and could uscles are one of the require a different approach. most important com- Mponents in the equine body. Without them, the horse would be unable to walk, chew food, digest it, or even The chiropractic swish his tail. Muscles com- adjustment con- prise the largest tissue mass in the horse’s body. There are various types of sists of a short, muscles performing a wide variety of duties, but ba- sharp thrust with sically they all function in the same general way—a period of contraction or shortening of muscle fibers, the hands to a spe- followed by a period of muscle relaxation or length- cific area of the ening of muscle fibers. back. A horse’s conformation and muscle types can determine Take-Home Message The equine back is a well-designed how well he can perform certain structure in the properly conformed horse. However, when poor conformation is in- tasks, but all horses are subject volved and/or inappropriate tack is used, serious problems can arise. h to muscle injury and disease

About the Author ustration Les Sellnow is a free-lance writer based near Riverton, LL In this article, we’ll take a look at how equine muscles Wyo. He specializes in articles on equine research, and he function and are nourished, as well as examine some of operates a ranch where he raises horses and livestock. He the problems that have surfaced, such as hyperkalemic has authored several fiction and non-fiction books, includ- in Peterson i B ing understanding equine Lameness, understanding the o periodic paralysis (HYPP) and tying-up. As has been the young Horse, and the Journey of the western Horse, r case throughout this series, we will draw on a wide variety Dr. published by Eclipse Press and available at www.Exclusively of sources, including textbooks. However, a couple of researchers deserve Equine.com or by calling 800/582-5604. specific mention. Much of the information concerning description of muscle further reading structure comes from a paper authored by Craig H. Wood, PhD, coordinator AAEP Convention 2005: “Treating Sore Backs Table of Distance Learning at the University of Kentucky, and published in the Topic,” www.TheHorse.com/emag.aspx?id=6537. Horse Industry Handbook. When we discuss HYPP, the work of Sharon “Fitting the Saddle to the Withers,” www.TheHorse. Spier, DVM, Dipl ACVIM, PhD, associate professor at the University of com/emag.aspx?id=5700. editor’s Note “Hunter’s Bump,” www.TheHorse.com/emag.aspx? California, Davis, becomes a source of information. No discussion on ty- This is the eighth in a 12-part series of articles on equine id=4649. anatomy and physiology. Future topics include the tendons ing-up should be conducted without drawing on the research of Stephanie “Understanding Back Pain,” www.TheHorse.com/ and ligaments, the digestive system, the circulatory and Valberg, DVM, PhD, professor of large animal medicine and director of the emag.aspx?id=3901. respiratory systems, and the reproductive system. Equine Center at the University of Minnesota.

34 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 35 Type 1 fibers do not that has been traced to a genetic defect in oxidize the muscle the Quarter Horse stallion Impressive. fuels rapidly and, as Earlier it was noted that muscles receive erg a result, are fatigue LB signals from nerves to react. As part of this resistant. They are process, a membrane “pore” or channel in anie Va

aerobic in nature, PH the muscle opens and closes, allowing for te which means they s exchange of the electrolyte sodium from utilize fuel in the outside to inside of the muscle cell. Proper Types of Muscles presence of oxygen. functioning of the sodium channel is vital Courtesy Dr. ustration

The three muscle classifications are Primarily, these fi- Skeletal muscle from a normal foal (left) compared to a horse with PSSM LL for electrical stimulation and contraction smooth, cardiac, and skeletal. The first two bers are used for (right). The PSSM horse has an accumulation of abnormal polysaccharide of the muscle fibers. are involuntary or automatic, which means long-term, non- (dark purple stains). In horses with HYPP, this channel does

they function as needed without having to strenuous work. The amount of adenosine triphosphate in Peterson i not function properly, and horses so afflict- B o be called into action for a specific need. By comparison, Type 2 fibers are fast- (called ATP, supplier of energy to cells in r ed often are characterized by intermittent r. Skeletal muscles are voluntary; the brain contracting (fast-twitch) and tend to burn the body) required by a working muscle is D episodes of muscle tremors, manifested sends a signal to the muscles via nerves, up muscle fuel in a hurry. As a result, they dependent on the effort being expended. Skeletal muscles are striated in design. A single muscle is composed of numerous muscle bundles by generalized or localized shaking, trem- and the muscles react accordingly. fatigue rapidly when compared to their For example, when a horse is just ambling made up of either Type 1 or Type 2 muscle fibers. bling, and weakness. In severe cases, the Non-skeletal muscles are basically the Type 1 counterparts. Type 2 fibers are fur- across the pasture at a slow walk, very little horse might suffer an episode of paralysis same for all horses. Smooth muscles are ther classified as Type 2A, Type 2B, and energy is required, and Type 1 fibers are be dissipated, the working muscles are the draft horse’s muscle structure adapt it that could cause its death through cardiac located in such places as the digestive tract, Type 2C. Type 2A fibers are recruited for utilized. The fuel for these muscle fibers is compromised, and the horse is fatigued. for power at the walk. arrest or respiratory failure. respiratory and circulatory systems, as well speed or an increase in strenuous activity. a combination of glycogen (the main form It is different when an endurance horse When walking, the draft horse is capable Tying-up (know as recurrent exertional as the urogenital system. These muscles Type 2B fibers are called on for sustained of carbohydrate storage), glucose (sugar), competes. It normally travels at slower of moving heavy loads. However, its muscle rhabdomyolysis) is another affliction of the are many and varied, and they respond to bursts of speed or effort that carry the and fat, with the emphasis on fat during speeds where muscles can rely heavily structure is not designed for it to travel at muscles. It generally is manifested in one stimuli within the respective systems. horse to the point where anaerobic ener- non-strenuous activity. However, when on aerobic energy generation. As a result, a high rate of speed. Conversely, the angu- of two forms. One form is called polysac- There are three major types of cardiac gy—the type provided without oxygen—is the horse breaks into a trot, the scenario when an endurance horse becomes fa- lar form, long legs, and well-muscled rear charide storage myopathy (PSSM) and has muscles: atrial muscle, ventricular muscle, required as an energy source. changes. Now, Type 2A fibers are recruited. tigued, it is often the result of glycogen de- quarters of the Thoroughbred allow it to been noted in Quarter Horses, Paints, Ap- and specialized excitatory and conductive Type 2B fibers contract with a maximum If speed is increased to a run, Type 2B fi- pletion—running out of fuel—rather than move fluidly at speed, but it does not have paloosas, draft horses, draft crosses, warm- muscle fibers. Cardiac muscle is controlled velocity that is 10 times that of Type 1 fibers bers might be brought into play. a build-up of lactic acid. the muscular strength to move heavy loads bloods, and a few Thoroughbreds. by the central nervous system. and three times that of Type 2A fibers. When this happens, more glycogen and/ at the walk. With PSSM, glycogen accumulates in Type 2C fibers are classified as transi- or glucose is needed as fuel through a pro- Oxygen for Fuel Within these respective groupings, how- the muscle, but the muscle is unable to uti- Skeletal Muscles tional and can serve as either a Type 2A or cess known as glycolysis. This involves the It quickly becomes apparent that the ever, conformational differences can have lize it. In essence, the muscle has an abun- The skeletal muscles are striated in de- Type 2B. Research has demonstrated that breaking down of glucose or glycogen into most important commodity for the equine a strong bearing on how efficiently the dance of fuel, but is unable to burn it to sign, with a single muscle being composed racing Thoroughbreds and Quarter Horses energy (ATP) without oxygen and, thus, is muscles to function appropriately is oxy- muscles function. produce energy. Minus the energy that the of numerous muscle bundles made up of have more Type 2 fibers than Type 1. an anaerobic reaction. Glucose is the end gen, even though a portion of its energy For example, a racehorse with straight glycogen is designed to supply, these horses muscle fibers. There are two general clas- It is estimated that 80-90% of the mus- product of carbohydrate metabolism and is might be produced anaerobically during shoulders and pasterns will have a short develop muscle cramps and stiffness. sifications for these muscles fibers: Type 1 cle fibers in Thoroughbreds and Quarter the chief source of energy for living organ- strenuous exercise. Oxygen is inspired stride. This means that the muscles must Treatment of horses with this affliction and Type 2. Horses are of the fast-twitch or Type 2 va- isms. Excess glucose is converted to glyco- into the lungs and is conveyed by the work harder via more frequent strides involves supplying them with alternative Generally speaking, the slow-contracting riety. Standardbreds and Arabians have an gen and is stored in the liver and muscles bloodstream to the working muscles. for this horse to reach a particular rate of sources of energy, such as a diet high in fat Type 1 fibers are utilized heavily by horses intermediate number, about 75%. A heavy for future use. The average, healthy horse at rest has no speed. Its counterpart, with appropriate rather than high in carbohydrates. involved in non-strenuous activity, while hunter or a draft horse, by comparison, Thoroughbreds travel at a high rate of trouble inspiring an appropriate amount of conformation, will have a fluid stride that There are more types of tying-up, some the fast-contracting Type 2 fibers are more would have a preponderance of Type 1, or speed during a race, with Type 2 muscle fi- oxygen to fuel the muscles, but things can will cover more ground and reach the same of which show up in excitable young racing often used by equines athletes, such as a slow-twitch, fibers. bers being recruited along the way. Because change rapidly when the horse is perform- rate of speed with much less effort. Thoroughbred fillies and might be genetic racing Thoroughbred or Quarter Horse. Training can have a bearing on muscle fi- this relatively high rate of speed requires ing at speed. Researchers have conducted Various disciplines also bring with them in origin. Wood writes that the muscle fibers con- ber composition. For example, the number a continued burst of energy, it isn’t long countless experiments using treadmills to certain muscle conformation requirements. tain several hundred to several thousand of Type 2A muscles fibers will increase in before the utilization of fat and glycogen measure the amount of oxygen the exercis- The cutting horse, for example, needs a Take-Home Message myofibrils. Each myofibril, in turn, has Thoroughbreds and Standardbreds as they stores by the muscles is unable to supply ing horse inspires. heavily muscled rear quarters because it is More is being learned about muscles and many myosin and actin filaments. These are trained to race at longer distances. all of the energy required and anaerobic These studies have revealed that the required to stop and pivot on its rear legs how they function. The good news about filaments are large polymerized protein glycolysis (without the presence of oxygen) strenuously exercising horse might be re- when preventing a cow from returning equine muscles is that they are adapt- molecules that are responsible for muscle TYPE 1 occurs with its more rapid burning of gly- quired to inspire up to 90 liters of oxygen to the herd. The same is true of a reining able. Through exercise and conditioning, contraction. cogen. The lactic acid that accumulates as per minute. horse, which is required to slide to a stop they can be prepared and conditioned for He also tells us that skeletal muscle con- the result of glycolysis can bring with it an To achieve this, the horse’s respiratory and spin. A roping horse that is used by a diverse activities in such a way that they tains a sarcoplasmic reticulum (calcium early onset of fatigue. rate might exceed 150 breaths per minute header in team roping, on the other hand, function efficiently and stave off fatigue in pump) and a tubular system. The calcium TYPE 2B We can compare lactic acid to exhaust (the normal range is 8-12 breaths per min- needs powerful muscles in the shoulders to order to avoid injury. h pump, Wood reports, is extremely impor- from a gasoline engine. Both lactic acid ute). turn a steer so that it is positioned for the D About the Author tant in muscle contraction through the oo and engine exhaust are by-products of fuels heeler to throw his loop. TYPE 2A w Les Sellnow is a free-lance writer based near Riverton, release and uptake of calcium ions, which being burned to provide energy. The gaso- Form and Movement Wyo. He specializes in articles on equine research, and he are involved in the contraction process. line engine must emit the exhaust in order Conformation is involved in the way that Injury and Disease operates a ranch where he raises horses and livestock. He Muscles are signaled to contract via to continue functioning properly. Likewise, muscles function and also is involved in de- Injury to muscles can limit their ability has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the nerve impulses. Relaxation occurs when the horse’s muscles must rid themselves of termining what disciplines are right for a to function properly. The same is true of young Horse, and the Journey of the western Horse, Courtsey Dr. Craig the nerve impulses cease. A cross section of Type 1 (slow-contracting) and lactic acid for optimal functionality. When particular individual. We have already indi- some afflictions that have surfaced. One of published by Eclipse Press and available at www.Exclusively Equine.com or by calling 800/582-5604. The slow-contracting or slow-twitch Type 2 (fast-contracting) muscle fibers. lactic acid accumulates faster than it can cated that the thickness and massiveness of them is HYPP. This is a muscular affliction

36 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 37 Type 1 fibers do not that has been traced to a genetic defect in oxidize the muscle the Quarter Horse stallion Impressive. fuels rapidly and, as Earlier it was noted that muscles receive erg a result, are fatigue LB signals from nerves to react. As part of this resistant. They are process, a membrane “pore” or channel in anie Va aerobic in nature, PH the muscle opens and closes, allowing for te which means they s exchange of the electrolyte sodium from utilize fuel in the outside to inside of the muscle cell. Proper Types of Muscles presence of oxygen. functioning of the sodium channel is vital Courtesy Dr. ustration

36 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 37 061019 OCD ad w photos.qxp 10/18/2006 3:18 PM Page 1

By Les seLLnow

endons and ligaments in the horse are the “belts” and “cables” that hold tendons & Tbones in place and allow the muscles to do their jobs in creating propulsion— forward, backward, sideways, and up and down. Because of the workload often put upon them, tendons and ligaments are fre- TM quent sites of injury and disease. ligaments What are tendons and ligaments? Dorland’s Illustrated Medical Dictionary: Tendon—A fibrous cord by which muscle is attached to bone. Ligament—A band of fibrous tissue that connects bones or cartilages, serving to Optimal Cartilage Development support and strengthen joints.

Many athletic horses suffer tendon and ligament injuries, Introducing the OCDTM Equine Advisory Board Every day more new clients experience dramatic results with OCDTM which can end a Pellets. The gentlemen below have participated as consultants in the competitive life if not development of the product. Their experience, their feedback and their advice have made a powerful difference for the company. handled quickly and effectively

To go into detail about every tendon and ligament would fill several textbooks, which is something that’s already been done. Instead, we will concentrate on the tendons and ligaments in the limbs, especially the forelimbs, which often are the sites of injury and disease. We will examine their construction, how they function, and what can happen when something goes awry. John Hayes Douglas R. Beebe, DVM Adrian Regan Once again, we’ve utilized multiple sources, including textbooks, but one source has been most helpful: Nathaniel White II, DVM, MS, Dipl. ACVS, director of the Mar- ion duPont Scott Equine Medical Center, part of Virginia Tech in Leesburg, Va.

Backed by a Injury and Performance The importance of maintaining healthy 75-DAY tendons and ligaments is borne from the fact that injuries to that part of the anato- Dramatic Results Guarantee my can quickly end a performance horse’s Call 800.815.6599 or visit www.ocdequine.com to receive $89 in free product. career, and has done so in a number of instances. One British researcher has estimated editor’s Note that more than 30% of horses involved This is the ninth in a 12-part series of articles on equine anatomy and physiology. Future topics include the diges- in racing and other forms of competition tive system, the circulatory and respiratory systems, and the throughout Europe suffer from some sort reproductive system. Dr. roBin Peterson of tendon injury or problem as the result of

By Les seLLnow

38 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 39 © 2006 OCDTM Equine. All rights reserved. to the short pastern bone (P2). t endonS and ligamentS that allow the muscles to function, they also Following is the numerical rating: Along the way, the superior check Forelimb Hindlimb serve as shock absorbers. Tendons can help Type 1 Tendon enlargement with lesions ligament connects the superficial dissipate concussion that otherwise would appearing only slightly hyperechoic (dark- flexor tendon to the radius just be borne by joints, bones, and muscles. er) than usual. They represent minimal above the knee. What we really have here is a rather elab- disruption of the fiber pattern and minimal The deep flexor tendon orate cable and pulley system that allows infiltration of inflammatory fluid. originates with the deep flexor the legs to move frontward and rearward Type 2 Lesions are approximately half muscle, also located behind the and, at the same time, supports the weight echoic and half anechoic. They represent lateral digital the vigorous exercise involved in running, elbow. It runs between the su- extensor tendon of the horse and absorbs concussion. All disruption of the fiber pattern and local in- jumping, and dressage. perficial flexor tendon and the extensor carpi superficial digital of the parts—bones, ligaments, cartilage, flammation. White has stated that he doubts the cannon bone and ultimately at- radialis flexor tendon and tendons—are designed to interact and Type 3 Lesions are mostly anechoic and common digital percentage would be quite that high in the taches to the coffin bone (P3). extensor tendon function efficiently. When injury or disease represent significant fiber tearing. United States, but feels it could very well be Along the way, the inferior check prevents this, the results can be dramatic. Type 4 Lesions are totally anechoic. They inferior check that high in the United Kingdom because ligament connects the deep flex- common digital ligament As the horse compensates for injury to one appear as black areas within a structure extensor tendon racehorses there usually compete on turf. or tendon with the cannon bone deep digital aspect of the apparatus, it might have a and indicate almost total fiber tearing with flexor tendon ing

The soft, yielding turf places substantial just below the knee. The role of harmful effect on the other components, hematoma (blood-filled) formation. V o

suspensory L y

stress on the tendons and ligaments. the check ligament is to limit ligament and they will be compromised as well. It is estimated that a tendon can stretch C

American horses, on the other hand, or “check” the movement of the annular Basically, there is a stress/strain rela- up to 8% before the fibers begin tearing. r. nan tend to sustain more joint and bone in- tendon so it isn’t over stressed. ligament tionship involved when the tendons are Ligaments are not immune to injury and D juries than their European counterparts The digital extensor tendon brought into play. Stress or load is applied disease. When injuries occur to ligaments when fatigue is combined with overstretching, a bowed tendon becomes a possibility. because American horses often race on begins with the digital extensor digital sesamoidean when the horse bears weight on each limb, in horses, they often involve the suspen- ligaments it eterson D harder dirt surfaces. muscle in the same general area P which is accommodated by an equivalent sory ligament. Unlike tendon injuries, liga- riding under saddle and swimming, can be re in C The wonder isn’t that tendons and liga- as the two flexor tendons, only B lengthening (strain) of the tendon. ment injuries often occur in both front and helpful in the remodeling phase of tendon oto oto r. ro

ments sustain injury, but rather that they on the forward (cranial) portion PH D During exercise, a horse’s tendons might rear limbs. healing. White says most racehorses can aren’t injured more often. With a Grand of the leg rather than the rear- stretch and retract from one to three start galloping after four to five months, but Prix jumper, for example, the tendons ward (caudal) side. It continues downward fetlock as the horse stands or moves. inches. When the tendon is pushed beyond Treatments the tendon should be monitored regularly of the foreleg are asked to do the near- along the front of the cannon bone all the At the fetlock, another ligament—the its “strain” capacity, injury is the result. Treatment of a tendon injury, according with ultrasound, using increased scrutiny impossible. The tendons often are stretched way past the pastern, ultimately attaching volar annular ligament—wraps around the The damage normally involves rupturing to White, is a combination of acute therapy when sprint work is initiated. Normally, he to the limit and beyond when a horse lands to the coffin bone. entire joint and attaches at the lower end of the tendon’s collagen fibers when they and long-term rehabilitation. The goal is to says, horses should not race before eight after clearing a six-foot jump. The flexor tendons are designed to of the third metacarpal bone and the up- are stretched beyond their capacity. This reduce inflammation, maintain blood flow, months after a Type 2 or greater injury. With move—or flex, as the term implies—the per edges of P1. One of its prime functions results in inflammation, soreness, and an and decrease the formation of scar tissue. some horses, tendons will not be ready for Cases in Point leg and hoof in a rearward motion, and is to keep the tendons in place. (When the inability of the limb to function normally. The initial therapy includes systemic and race-type stress until 12 to 14 months after Deep digital flexor tendons and the su- the extensor tendons allow the limbs to be deep flexor tendon is injured, it quite often Most serious tendon injuries occur to local anti-inflammatory therapy. Phenylbu- the injury. perficial flexor tendons play important brought forward, or extended. A greater is at this point. Many practitioners say that the front limbs for obvious reasons. First, tazone therapy for five to seven days is in- Research continues in an effort to find roles in the horse’s movement. As does the stress is placed on the flexor tendons than this is the most difficult tendon injury to 60-65% of the horse’s weight is carried on dicated, and the anti-inflammatory DMSO more effective treatment approaches for suspensory ligament, which originates on the extensors. deal with because it’s encased in a strong the front end. Second, when a horse travels is applied topically for seven to 10 days. Ice tendon injuries. New treatment methods at the upper end of the third metacarpal As the horse’s weight descends, the tendon sheath.) at speed, there is one point in every stride or cold water is applied for the first seven include shock wave therapy and the use bone and the lower edges of the distal row knee joint is straight or even overextend- While the digital muscles provide the where the animal’s entire weight descends to 10 days, depending on the amount of of hyperbaric oxygen chambers. Both ap- of carpal bones. ed (bent backward), stretching the flexor power to raise, lower, and bend the legs at on a single foreleg. This translates into ex- swelling. proaches have produced some positive re- Tendons and ligaments are similar in tendons, but putting less pressure on the the knee, ankle, or hock, the tendons are traordinary strain on the flexor tendons in The injection of hyaluronate acid around sults, but more research is needed. Interest structure, but, generally speaking, tendons extensors. Most tendon injuries and dis- the real workhorses. Each time a horse that leg as well as on the entire suspensory the tendon or administered intravenously in using stem cells of bone marrow origin are more flexible and have more stretching ease involve the two flexor tendons, with takes a step, the tendons and ligaments apparatus. The same is true of Grand Prix can also have beneficial anti-inflammatory (not embryonic) to stimulate tendon and capability. Both are made up of collagen the superficial flexor tendon being the one come into play. In addition to providing jumpers when they land and all of the con- effects, according to White. ligament healing is also growing. fibers that are arranged lengthwise so that most apt to “bow” or suffer inflammation. flexion, they serve as part of the stay appa- cussion is absorbed by the front legs. Another important aspect of acute treat- they are capable of stretching. The reason the word “bow” is used is ratus that allows a horse to stand and even When injury occurs, there often is great ment, says White, involves providing sup- Take-Home Message Collagen is the tough protein substance that when the fibers tear, inflammation sleep on its feet. variation as to severity. The rule of thumb port for the injured tendon in the form of Tendon and ligament injuries often go found in skin, tendons, bone, cartilage, and swelling cause the tendon to bulge or is the more fibers that are torn, the more wraps or bandages. But, they must be prop- hand in hand with horses involved in vigor- ligaments, and all other connective tissues, bow outward. Tendon Injury serious the injury and the longer the heal- erly applied. Adequate padding is a must to ous athletic pursuits. However, many ten- including fascia (flat layers of fibrous tis- Another important part of the leg ap- Each tendon is enclosed in a sheath. ing and recuperation period will be. avoid further injury from constriction of don and ligament injuries can be avoided sue that seperate different tissue layers). paratus is the suspensory ligament. It at- Thinner areas of the sheath, such as the ar- the already injured tendon. through proper conditioning and training Collagen allows tendons and ligaments to taches to the cannon bone just below the ea behind the cannon bone, are often sites Diagnosing Injuries Rest is the primary treatment, accord- regimens and by not pushing a horse be- stretch and contract and also gives them knee and passes downward (distally), at- of injuries. A thick sheath encases the ten- Tendon injuries today can be examined ing to White. He says stall rest with hand yond its limits in racing or other competi- their toughness. taching at the sesamoid bones at the rear dons at the point where they pass behind with ultrasound. The severity of defects or walking is normally required for the first tions. h The superficial flexor tendon is most of the fetlock joint. At the bottom of the the fetlock. It would appear that nature has lesions in the injured tendon is rated on a one to two months after the injury. Further About the Author readily visible because it runs down the sesamoids the ligament splits into extensor provided additional protection for the ten- scale of one to four, according to how they increases in activity, White says, are deter- Les Sellnow is a free-lance writer based near Riverton, back of the cannon bone close to the skin. or sesamoidean ligaments that wrap around don at this point because this is where there appear on the ultrasound images. Lesions mined by the ultrasonic appearance of the Wyo. He specializes in articles on equine research, and he It originates at the superficial flexor muscle to the front of the long pastern bone (P1). is the most friction and pressure, especially appear as an ultrasound echo termed a hy- tendon. The core lesion should diminish operates a ranch where he raises horses and livestock. He just behind the elbow in the front legs and The suspensory ligament is vital for sup- when the horse is traveling at speed. The perechoic (partial loss of echoes) or an an- within the first two months, followed by has authored several fiction and non-fiction books, including understanding equine Lameness, understanding the just behind the stifle in the rear limbs. It porting the fetlock. When abnormalities or sheath is lubricated with synovial fluid to echoic (total loss of echoes) region, usually decrease in the cross-sectional area. young Horse, and the Journey of the western Horse, travels downward, splitting after it passes injuries occur that weaken the suspenory eliminate friction as the tendon moves. in the center of a tendon. The greater the Turnout is often recommended, but in published by Eclipse Press and available at www.Exclusively over the sesamoid bones, and attaches ligament, there often is a dropping of the While we think of the tendons as cables loss of echoes, the more severe the injury, some cases, controlled exercise, including Equine.com or by calling 800/582-5604.

40 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 41 to the short pastern bone (P2). t endonS and ligamentS that allow the muscles to function, they also Following is the numerical rating: Along the way, the superior check Forelimb Hindlimb serve as shock absorbers. Tendons can help Type 1 Tendon enlargement with lesions ligament connects the superficial dissipate concussion that otherwise would appearing only slightly hyperechoic (dark- flexor tendon to the radius just be borne by joints, bones, and muscles. er) than usual. They represent minimal above the knee. What we really have here is a rather elab- disruption of the fiber pattern and minimal The deep flexor tendon orate cable and pulley system that allows infiltration of inflammatory fluid. originates with the deep flexor the legs to move frontward and rearward Type 2 Lesions are approximately half muscle, also located behind the and, at the same time, supports the weight echoic and half anechoic. They represent lateral digital the vigorous exercise involved in running, elbow. It runs between the su- extensor tendon of the horse and absorbs concussion. All disruption of the fiber pattern and local in- jumping, and dressage. perficial flexor tendon and the extensor carpi superficial digital of the parts—bones, ligaments, cartilage, flammation. White has stated that he doubts the cannon bone and ultimately at- radialis flexor tendon and tendons—are designed to interact and Type 3 Lesions are mostly anechoic and common digital percentage would be quite that high in the taches to the coffin bone (P3). extensor tendon function efficiently. When injury or disease represent significant fiber tearing. United States, but feels it could very well be Along the way, the inferior check prevents this, the results can be dramatic. Type 4 Lesions are totally anechoic. They inferior check that high in the United Kingdom because ligament connects the deep flex- common digital ligament As the horse compensates for injury to one appear as black areas within a structure extensor tendon racehorses there usually compete on turf. or tendon with the cannon bone deep digital aspect of the apparatus, it might have a and indicate almost total fiber tearing with flexor tendon ing

The soft, yielding turf places substantial just below the knee. The role of harmful effect on the other components, hematoma (blood-filled) formation. V o suspensory L y

stress on the tendons and ligaments. the check ligament is to limit ligament and they will be compromised as well. It is estimated that a tendon can stretch C

40 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 41 Understanding the equine digestive system AAEVTAAEVT can make your horse healthier and give you fewer worries about food gastric upset The American Association of Equine Veterinary Technicians and Assistants Factory www.aaevt.org By Les seLLnow

he equine digestive system is a complicated WHO WE ARE: The American Association of Equine Veterinary factory that is designed to process small Tamounts of food frequently and convert Technicians & Assistants (AAEVT) is a sister organization to the them into nutrients that can be absorbed and American Association of Equine Practitioners (AAEP). We are a produce energy. The same, concerning the end result, could be said of the cow, pig, dog, cat, separate, non-pro t corporation whose membership consists of or even man. But, the horse’s digestive sys- technicians, assistants, practice managers and support staff from all tem is unique, and perhaps more prone to problems than most others. aspects of equine veterinary medicine. This is not because of poor design, Wisconsin meeting 2004 but is the result of humans changing what nature intended for the horse. OUR MISSION: To promote the health and welfare of the horse In the wild, horses have little to do through the education and professional enrichment of the equine but eat, stay out of the way of predators, and procreate. This means they range veterinary technician and assistant. across the countryside, selecting immature forages that are easy to digest. They graze as they roam, MEMBERSHIP: Open to all equine veterinary technicians, consuming small amounts of food assistants, practice managers, support staff, students, and throughout the day and even at night. Under this scenario, there international member are welcome as well. Kentucky meeting 2006 are few digestive problems. However, man has altered Nature’s scheme. First, he often BENEFITS: Members receive quarterly newsletters, full access to adds workloads that require more the web site, on-line articles and up-to-date information, discounted than just grass to provide the necessary nutrition. Second, in many cases, all registration at our regional CE meetings and the annual AAEP/ choices have been taken from the horse. AAEVT meeting, NTRA bene ts, and eligibility to participate in He no longer roams at will, picking out the AAEVT on-line certi cation program or choice spots for grazing. Instead, he is ustrations confined to pastures or paddocks where iLL become a member of the AAEVT Academy. there might be little to choose from in the way of food. He eats what is there or

in Peterson is provided by his caretakers. B o r Because his owners or caretakers often Dr. have busy schedules, the horse no longer For more information and to become a member, editor’s Note is able to eat small amounts frequently. In- This is the tenth article in a 12-part series on equine anat- stead, he usually is fed a large quantity of please visit our web site at omy and physiology. Future topics include the circulatory food, and that sometimes occurs only once and respiratory systems and the reproductive system. www.aaevt.org each day.

42 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 43 Understanding the equine digestive system AAEVTAAEVT can make your horse healthier and give you fewer worries about food gastric upset The American Association of Equine Veterinary Technicians and Assistants Factory www.aaevt.org By Les seLLnow

42 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 43 day when grazing. This amount, of course, another strong argument for frequent use in the digestion of fats and amino acids. Horses are susceptible to a variety of ail- The microbial populations within the will be dramatically decreased when the meals containing small quantities of feed. However, when the stomach is empty, the ments, including colic, if they ingest toxic cecum become specific for digestion of horse is confined and fed hay and grain. Food passes through the stomach quite acid attacks the unprotected squamous cells materials. The reason is basic. With cows, the type of food that the horse normally Incidentally, the way in which a horse quickly. In fact, by the time a horse has in the saccus caecus region of the stomach the action within the rumen can detoxify ingests. It’s very important to change a is fed can have a profound bearing on the finished with a meal, under some circum- (the non-glandular area of the stomach). feed before it reaches the small intestine. horse’s diet gradually in order to give the condition of the teeth that are used for stances, the first part of the meal consumed These attacks frequently result in the With the horse, this is not an option and microbes an opportunity to adjust, which grinding. Because there is not as full a jaw might already be leaving the stomach. That horse developing ulcers that can affect the the toxic material lands in the small intes- could take several weeks. sweep when consuming hay and grain as time often is as little as 15 minutes. While animal’s performance, appetite, and/or be- tine in an unaltered state and is absorbed Microbial digestion continues in the What all this adds up to is an assault on when grazing, the confined horse often de- in the stomach, the food is mixed with pep- havior. into the bloodstream before it can be de- large colon. A large share of the nutrients the horse’s digestive system that it typically velops sharp edges that can hinder proper sin (an enzyme utilized in the digestion toxified. that result from microbial digestion ab- can’t handle, and problems such as colic chewing. of protein) and hydrochloric acid (which Small Intestine sorbed here are B-group vitamins, and founder can be the result. helps to break down solid particles). The partially digested food from along with some minerals and phos- The good news is researchers have been Esophagus The stomach has three main regions— the stomach passes into the small in- saccus caecus region phorus. at work to return horse feeding to a proper The esophagus is a simple muscular tube saccus caecus, fundic, and pyloric. The sac- testine that represents approximately It is in the large colon that a “twist- balance. There is information available that is between 50 and 60 inches in length, cus caecus region is located near the spot 28% of the horse’s digestive system. esophagus ed gut” usually occurs. The large co- about nutrient needs for various levels of and it conveys food from the mouth to the where the esophagus enters the stomach. It Basically, the small intestine is the lon consists of right and left ventral activity and conditions. For example, the stomach. When the horse is consuming is here where hydrochloric acid first mixes tube that connects the stomach with duodenum colons and the dorsal colon. The working horse has different requirements grass and even hay, few problems involving with food and slows the fermentation pro- the large intestine. On average, it is ventral colons have a sacculated con- than one turned out to pasture, and the the esophagus occur. However, when fed cess that began with the release of soluble about 70 feet long and three to four struction, which means there are a lactating mare has different needs than the crunch items, such as carrots or apples, sugars from the food in the horse’s mouth. inches in diameter when distended. It series of pouches involved. The struc- gelding being used for trail riding. there can be problems with pieces becom- It is important that there is very little fer- has a capacity of about 12 gallons. ture is designed to efficiently digest pylorus There also is a strong and growing em- ing lodged if the horse does not masticate mentation in the stomach as it will cause Although there are few similari- large quantities of fibrous materials, phasis on frequent feeding of small amounts (grind or crush) the food properly. the formation of gas, and the horse has ties between the digestive systems of pyloric but the pouches or sacs can become of feed instead of large single portions. The same can happen when consuming little capability to belch or otherwise dis- cows and horses, the small intestine region twisted and can fill with gas during

In this article on the digestive system, grain if the horse “bolts” food (consumes sipate accumulating gas. of each has about the same capacity. ustration the fermentation process. The result, we’ll take a look at just how this “factory” its food in a hurry) without chewing it The second area is the fundic region. However, the cow’s small intestine is LL in either case, can be a serious case is designed and how it functions. Knowl- properly. Because the horse has very little There the level of fermentation decreases nearly twice as long, but only about of colic. eterson i edge of the factory is step number one in reflux capability, choking on food can have even more. The third and final area is the half as wide in diameter. fundic region P By the time food reaches the small in B

o colon, nearly all of the nutrients have deciding how nutrient needs can be met serious consequences. pyloric region, where the stomach joins the It is in the small intestine of the r . r for individual animals. small intestine. At this point the fermenta- horse that serious digestive processes D been digested. Basically, what re- Stomach tion has almost ceased, but protein diges- take place. The intestine itself secretes mains is matter that is not digestible The Mouth The stomach of the horse is very small tion increases. enzymes to facilitate the process, but the Large Intestine by the horse. The prime function of the A discussion of the digestive system in relation to the overall size of the animal, Still another argument in favor of fre- prime supplier is the pancreas, which pro- There are five basic parts to the large in- small colon is to reclaim excess moisture must begin with the mouth, because it is and it makes up only about 10% of the ca- quent feeding of small amounts of food is vides enzymes that break down proteins, testine. They are the cecum, which is about and return it to the body. In the process, here that digestion gets under way. pacity of the entire digestive system. The that the stomach does not do well when fats, starches, and sugars. four feet long and one foot in diameter; the fecal balls are formed, which can be passed There are three salivary glands in the stomach can vary in size from eight to 16 empty. There are strong acids at work in Pancreatic enzymes help digest the food large colon, which is about 12 feet long through the rectum and are expelled out horse’s mouth, which can produce up to 10 quarts. However, it appears to function the stomach, but when there is an even flow while carbohydrates digest sugars and and 10 inches in diameter; the small colon, the anus. gallons of saliva per day. A prime purpose best when only about three-quarters full— of food, the stomach acid is put to positive starches, and proteases break proteins which is about 10 feet long and four inches The whole process of ingesting food, di- of saliva is to mix with the down into amino acids. At the same time, in diameter; the rectum; and the anus. gesting it, and expelling waste material can feed being consumed so it can small intestine lipases and bile from the liver are added to The cecum can hold eight to 10 gallons take from 36 to 72 hours on average. be formed into what amounts emulsify fats (make globules and suspend of food and water. It is in the cecum that to moist, loosely formed balls small colon them as particles) in water. undigested food from the small intestine, Take-Home Message that are easily swallowed. The horse does not have a gall bladder such as hay and grass, is broken down. The horse’s digestive system is a complex There are two ingredients stomach (which stores bile), so bile from the liver The cecum is an odd-shaped organ with grouping of organs that is designed for the in saliva that help to launch flows directly into the small intestine. both the entrance and the exit being at the free-grazing animal. Because of man’s con- the digestive process. One in- Once the digestive process in the small top. Food enters at the top, is processed, straints on the movement and feed choices gredient is bicarbonate, which intestine reaches a state of completion, and then leaves the cecum by the same of domestic horses, problems can arise. anus buffers and protects against the food is absorbed through the walls of route. If a horse consumes a heavy diet of Horse owners who understand how the amino acids in the stomach. the small intestine and is carried off by the dry food matter without adequate water, digestive system works can better manage Saliva also contains small bloodstream. Between 30-60% of carbohy- impaction can occur in the lower end of their horse’s feeding in order to get the best amounts of the enzyme amy- large colon drate digestion and absorption, and almost the cecum, which can cause colic. nutrition, with the least number of compli- lase. This ingredient assists rectum esophagus all amino acid absorption, occur in the The cecum and other components of the cations. H with carbohydrate digestion. small intestine. In addition, vitamins A, D, large intestine contain active populations When on pasture, the eating E, and K are absorbed in the small intes- of bacteria and microbes that break down About the Author process begins when the horse tine, as are some minerals, such as calcium food through a fermentation process. Food Les Sellnow is a free-lance writer based near Riverton, grasps grass by using a combi- ustration and some phosphorus. will remain in the cecum for up to seven Wyo. He specializes in articles on equine research, and he LL nation of the lips, tongue, and It generally takes food 30 to 90 minutes hours, allowing the bacteria and the mi- operates a ranch where he raises horses and livestock. He teeth. It was estimated by one to pass through the small intestine. The crobes to handle their phase of the diges- has authored several fiction and non-fiction books, includ-

eterson i ing understanding equine Lameness, understanding the researcher that the average P faster the food moves through the small tive process. Vitamins and fatty acids that cecum in young Horse, and the Journey of the western Horse, B

o published by Eclipse Press and available at www.Exclusively horse will take about 60,000 r intestine, the less time there is for the en- result from the fermentation process are Equine.com or by calling 800/582-5604. “jaw sweeps” (chewings) per Dr. zymes to perform their digestive tasks. absorbed in the cecum.

44 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 45 day when grazing. This amount, of course, another strong argument for frequent use in the digestion of fats and amino acids. Horses are susceptible to a variety of ail- The microbial populations within the will be dramatically decreased when the meals containing small quantities of feed. However, when the stomach is empty, the ments, including colic, if they ingest toxic cecum become specific for digestion of horse is confined and fed hay and grain. Food passes through the stomach quite acid attacks the unprotected squamous cells materials. The reason is basic. With cows, the type of food that the horse normally Incidentally, the way in which a horse quickly. In fact, by the time a horse has in the saccus caecus region of the stomach the action within the rumen can detoxify ingests. It’s very important to change a is fed can have a profound bearing on the finished with a meal, under some circum- (the non-glandular area of the stomach). feed before it reaches the small intestine. horse’s diet gradually in order to give the condition of the teeth that are used for stances, the first part of the meal consumed These attacks frequently result in the With the horse, this is not an option and microbes an opportunity to adjust, which grinding. Because there is not as full a jaw might already be leaving the stomach. That horse developing ulcers that can affect the the toxic material lands in the small intes- could take several weeks. sweep when consuming hay and grain as time often is as little as 15 minutes. While animal’s performance, appetite, and/or be- tine in an unaltered state and is absorbed Microbial digestion continues in the What all this adds up to is an assault on when grazing, the confined horse often de- in the stomach, the food is mixed with pep- havior. into the bloodstream before it can be de- large colon. A large share of the nutrients the horse’s digestive system that it typically velops sharp edges that can hinder proper sin (an enzyme utilized in the digestion toxified. that result from microbial digestion ab- can’t handle, and problems such as colic chewing. of protein) and hydrochloric acid (which Small Intestine sorbed here are B-group vitamins, and founder can be the result. helps to break down solid particles). The partially digested food from along with some minerals and phos- The good news is researchers have been Esophagus The stomach has three main regions— the stomach passes into the small in- saccus caecus region phorus. at work to return horse feeding to a proper The esophagus is a simple muscular tube saccus caecus, fundic, and pyloric. The sac- testine that represents approximately It is in the large colon that a “twist- balance. There is information available that is between 50 and 60 inches in length, cus caecus region is located near the spot 28% of the horse’s digestive system. esophagus ed gut” usually occurs. The large co- about nutrient needs for various levels of and it conveys food from the mouth to the where the esophagus enters the stomach. It Basically, the small intestine is the lon consists of right and left ventral activity and conditions. For example, the stomach. When the horse is consuming is here where hydrochloric acid first mixes tube that connects the stomach with duodenum colons and the dorsal colon. The working horse has different requirements grass and even hay, few problems involving with food and slows the fermentation pro- the large intestine. On average, it is ventral colons have a sacculated con- than one turned out to pasture, and the the esophagus occur. However, when fed cess that began with the release of soluble about 70 feet long and three to four struction, which means there are a lactating mare has different needs than the crunch items, such as carrots or apples, sugars from the food in the horse’s mouth. inches in diameter when distended. It series of pouches involved. The struc- gelding being used for trail riding. there can be problems with pieces becom- It is important that there is very little fer- has a capacity of about 12 gallons. ture is designed to efficiently digest pylorus There also is a strong and growing em- ing lodged if the horse does not masticate mentation in the stomach as it will cause Although there are few similari- large quantities of fibrous materials, phasis on frequent feeding of small amounts (grind or crush) the food properly. the formation of gas, and the horse has ties between the digestive systems of pyloric but the pouches or sacs can become of feed instead of large single portions. The same can happen when consuming little capability to belch or otherwise dis- cows and horses, the small intestine region twisted and can fill with gas during

44 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 45 SUCCEED® DIGESTIVE HEALTH PERFORMANCE SERIES By Les seLLnow

here are few similarities between horses and automobiles, but in a Tmanner of speaking, the horse’s cir- Of culatory and respiratory systems consti- “His extension scores are tute its engine. The food a horse consumes blood is its fuel. The fuel is converted into nutritional energy that powers the muscles. better than I thought were The respiratory system provides oxygen to facilitate metabolism, and the cardiovascular or circulatory system delivers the even possible for him.” oxygen and nutrients to tissues as well as & breath carrying off waste products that are pro- How digestive health can affect a horse’s movement. duced when the “engine” is running. The circulatory and respiratory We’ll take a close a look at these two systems and the manner in which they systems work together to fuel the function. horse’s body Steffen Peters needs no introduction situation that isn’t natural. And that can among Dressage riders and enthusiasts. keep them from looking and performing Respiratory System His performance aboard Floriano at to potential.” The purpose of the respiratory system the 2006 World Equestrian Games in can be stated simply and succinctly: It This point became even more obvious Aachen, Germany, helped the U.S. team functions to exchange oxygen and carbon in mid-2006 when Shannon and Luxor win the bronze medal in the Dressage dioxide. Oxygen is inspired for use by the achieved their highest scores ever competition. tissues, and carbon dioxide (CO2) is ex- – 74.5% in Prix St. Georges and 73.5% haled as a waste product. What is perhaps less well-known is how in Intermediaire I. In addition to those Steffen and Shannon Peters learned The amount of oxygen required and the hard he and his wife Shannon have collective marks, Luxor received scores of volume of CO produced varies with the that digestive health can help, or hinder, 8 and 9 for his extensions. 2 worked to reach and remain at such a performance. level of exercise. During intense exercise, high level. Even with great horses, the “I just assumed he could never do that. For him to feel the tissues require a great deal more oxy- best training and care, and an unending determination, the comfortable enough to engage himself that much more to gen than when the horse is at rest, and, Peters were searching for more. score an 8 or a 9 really shows that he’s able to stretch his strenuous exercise, of course, means more “Our horses were in top competition shape, so it’s not muscles without discomfort.” CO2 must be removed. To accomplish all like any of them looked poor,” says Shannon. “But there’s that is required during exercise involves Although horses are large, powerful animals, their digestive always room for improvement.” an increased respiration rate. tracts maintain a delicate balance that can be easily altered by Before we get involved with that, let’s the challenges of the performance lifestyle. The horse’s large And while Steffen and Floriano are competing on a world take a look at how air is inspired and pro- stage, Shannon is right behind them with her mount, Luxor. intestines, which represent about 75% of the total volume of cessed by the equine respiratory system. the GI tract, sit directly in front of the hind legs. For dressage, It all starts with the nostrils. There has “Luxor always scored consistently in the 7s for his a horse’s back muscles must be supple and loose to support extensions,” says Shannon. “With some horses, a score of 7 the dramatic collections and extensions required in long been casual debate on whether the is just the extent of their natural ability and they’re not able competition. Any level of discomfort or imbalance in the gut size of a horse’s nostrils influences the to improve beyond that. That’s where I thought Luxor was… can restrict these critical hind leg movements. amount of air inspired. Some would argue somewhere in the 7s.” that nostrils that can flare widely are ca- “Certainly what you feed your horses has a direct impact on pable of inspiring a greater quantity of air, But in late 2005, Shannon discovered a product called condition and performance. We do the best we can to keep while others will say that there is no sci- SUCCEED® Digestive Conditioning Program.® our horses healthy, despite training and travel schedules that entific evidence to prove that point. What- “I’m always trying new things, and trying to learn new can be quite intense. So for us, SUCCEED is a critical element ever the case, the air passes through the of overall health and condition.” nostrils and along a rather lengthy nasal ustration things. I didn’t really think about digestive health until iLL something went wrong. But this was different.” cavity. The fact that the horse’s nasal cavity is longer than most species provides Shannon tried the product, and the results surprised her. in Peterson

an assist during cold weather because the B o

“I didn’t expect to see the quality of changes I saw in their r cavity helps warm the air before it reaches

coats, weight and especially their trainability. We’ve also Dr. the lungs. noticed that our horses are better able to stretch and loosen The air then passes over the larynx and their muscles, leading to better collection.” pharynx. When everything is working as editor’s Note Both Shannon and Steffen were learning that maintaining it should, there is a smooth flow of air or This is the eleventh article in a 12-part series on equine optimal digestive health can beneﬁ t every horse, in ways food through this general area. When the anatomy and physiology. Next month’s topic is the repro- Available from select tack and feed stores, or ask your veterinarian. ductive system (stallions and mares) . they hadn’t considered. “It’s true that even the best care To locate a dealer or for more information, call toll-free 866-270-7939. horse swallows food, the pharynx and soft and feeding may not be enough. Even the best horses… palate are positioned so food is moved if we use them for performance, we’re keeping them in a www.SucceedDCP.com into the esophagus rather than the trachea. trachea. The larynx also functions as bar- After passing through the trachea, the When the horse is breathing, but not swal- rier to prevent food from entering the tra- inspired air arrives at the bronchial trees lowing, there is an open channel into the chea. within the lungs. The conducting airways

Photos © 2007, Stuart Vesty SUCCEED® and Digestive Conditioning Program® are registered trademarks of Freedom Health, LLC. ©2007. All Rights Reserved. PATENT PENDING. December 2006 The horse www.TheHorse.com 47

Peters Ext REV 1599.indd 1 3/15/07 2:07:48 PM SUCCEED® DIGESTIVE HEALTH PERFORMANCE SERIES By Les seLLnow

an assist during cold weather because the B o

“I didn’t expect to see the quality of changes I saw in their r cavity helps warm the air before it reaches coats, weight and especially their trainability. We’ve also Dr. the lungs. noticed that our horses are better able to stretch and loosen The air then passes over the larynx and their muscles, leading to better collection.” pharynx. When everything is working as editor’s Note Both Shannon and Steffen were learning that maintaining it should, there is a smooth flow of air or This is the eleventh article in a 12-part series on equine optimal digestive health can beneﬁ t every horse, in ways food through this general area. When the anatomy and physiology. Next month’s topic is the repro- Available from select tack and feed stores, or ask your veterinarian. ductive system (stallions and mares) . they hadn’t considered. “It’s true that even the best care To locate a dealer or for more information, call toll-free 866-270-7939. horse swallows food, the pharynx and soft and feeding may not be enough. Even the best horses… palate are positioned so food is moved if we use them for performance, we’re keeping them in a www.SucceedDCP.com into the esophagus rather than the trachea. trachea. The larynx also functions as bar- After passing through the trachea, the When the horse is breathing, but not swal- rier to prevent food from entering the tra- inspired air arrives at the bronchial trees lowing, there is an open channel into the chea. within the lungs. The conducting airways

Peters Ext REV 1599.indd 1 3/15/07 2:07:48 PM between the ribs) muscles and diaphragm oxygen—at least for a limited time—when intake, often referred to as “roaring.” The are called on to expand the chest, which, in the heart rate is 180 beats per minute or technical term is laryngeal hemiplegia (or turn, allows for expansion of the lungs. The less. When the heart rate is beyond that left laryngeal hemiplegia since it occurs base lung expansion allows for a greater quan- point, it is only a matter of time before the most often on the horse’s left side, the ex- trachea tity of air to be inspired. system will begin to falter. act cause for this is unknown). The amount of air inspired and expired There are many other problems that with each breath is called tidal volume. As Limiting Problems can affect the intake and exchange of air indicated, the number of breaths taken per Unfortunately, there are circumstances in the horse’s respiratory system. The bot- main alveolar minute is referred to as respiration rate or other than exercise that affect the amount tom line is that healthy lungs and airways bronchus sacs of the bronchial tree divide into smaller respiration frequency. Still another term of oxygen that can be utilized. are important, especially to the exercising and smaller bronchi. When cartilaginous involved is minute volume. Simply put, rAo One of the most troublesome con- horse. apex caudal plates are no longer present in the walls of this is the amount of air inspired and ex- ditions that affect respiration is recurrent lobe the smallest bronchi, the airway is termed pired in one minute. airway obstruction, or heaves, formerly Cardiovascular System apical lobe a bronchiole. The bronchioles, in turn, join The change in minute volume during known as chronic obstructive pulmonary We turn now to the cardiovascular or heart Dr. roBin Peterson iLLustration with the alveolar ducts that terminate in exercise can be dramatic. During rest, for disease (COPD). Basically, RAO is inflam- circulatory system of the horse. This con- the functional units of the lungs where gas example, the minute volume for a normal mation of the small bronchioles in the sists of blood, blood vessels through which exchange actually occurs—the alveoli. horse might be 150 liters per minute. Dur- lungs. When RAO strikes, the lower airway the blood flows, and the heart that provides The alveoli are small out-pouchings ing a fast gallop, this can quickly increase system is unable to function effectively. power for the flow of blood. throughout the body. increased, the horse’s heart rate goes up so along the walls of the alveolar sacs and al- to 1,500 liters per minute. Because minute The inflammation serves to develop ob- The normal adult horse weighing 1,000 Thus, it becomes obvious that the prime that more oxygen and nutrients can be de- veolar ducts. It is through the walls of these volume is a combination of respiration rate structions within the delicate airways and pounds will have about 13.2 gallons of function of the circulatory system is to livered to the tissues. The heart rate, quite tiny pouches that gas exchange takes place. and tidal volume, a horse can increase it air is unable to flow freely. As the condition blood in its body. The blood is composed deliver oxygen to tissues throughout the simply, is the number of times a horse’s The exchange occurs between air within al- either by breathing faster, breathing more worsens, more and more physical effort is of red blood cells (erythrocytes), white body, along with nutrients absorbed from heart beats during a minute. veoli and blood within the capillaries in the deeply, or both. involved when the horse inspires air. blood cells (leukocytes), platelets, and liq- the digestive system. It also acts as some- When a horse is at rest, his heart rate alveolar walls. However, there is a limit to the min- Recurrent airway obstruction can be uid (plasma). thing of a garbage disposal by delivering might be as low as 25 beats per minute. The alveoli have very thin walls between ute volume that can be achieved during caused by a number of conditions, with As indicated in the discussion on the the end products of cellular metabolism to When he is exercising at the maximal rate, oxygen-laden air in the lungs and the blood maximal exercise. When the horse is at a dusty hay and a dusty environment often respiratory system, the red blood cells the lungs and kidneys for removal. the heart rate can shoot as high as 250 vessels that contain red blood cells that will maximum exercise level—a heart rate that being implicated. have an iron-containing protein known The circulatory system also fills another, beats per minute. Obviously, the horse can carry oxygen to tissues throughout the body. has reached 200 beats per minute and be- eIPh Still another condition is known as hemoglobin, which binds oxygen for less spectacular role by helping to dissipate sustain this type of effort for only a short It is at this point that the two systems— yond—the blood leaving the lungs might as exercise-induced pulmonary hemor- transportation to the tissues. This is the heat by diverting blood toward the skin period of time. When the heart is beating respiratory and circulatory—join forces. not be carrying enough oxygen to ade- rhage (EIPH). Simply put, this condition primary function of the red blood cells. surface during exercise. at about 250 beats per minute, the cardiac The oxygen binds to hemoglobin for trans- quately service the tissues. This condition involves the presence of blood in the re- The main role for the white blood cells is Earlier, we pointed out that when exer- output is at the rate of approximately 55 port by the circulatory system to the tis- is referred to as arterial hypoxia. Generally spiratory tract during exercise. Horses to work with the rest of the immune sys- cise levels increase, so does the horse’s res- gallons of blood being pumped by the heart sues. speaking, the respiratory system can de- with this condition often are referred to tem to defend against bacterial invasions. piration rate. The same is true for the circu- per minute. The oxygen-laden red blood cells carry liver the re- as “bleeders.” The condition shows up in Platelets function in the blood clotting pro- latory system. As demands on the body are Another term utilized in discussions of their valuable product to the tissues, quired racehorses more than in any other disci- cess. where cell metabolism occurs and pline, although it can be found after any The key element in the en- coronary aortic valve CO2 is produced. The blood then strenuous exercise. tire vascular system, of course, EqUINE HEART groove heads back to the lungs via the roaring The larynx, which plays an im- is the heart, whose job it is to aorta pulmonary aorta pulmonary veins, but this time it is loaded portant role in the eating/breathing pro- pump blood through the cir- brachiocephalic veins cranial vena veins trunk cava with more CO2 than oxygen. cess, also can cause problems. In some culatory system. The flow of How much oxygen is taken in horses, the larynx does not open com- blood is through a system of and how much CO2 is expired pletely when the horse is breathing. blood vessels. When blood is depends on the amount of exer- In addition to limiting the pumped from the heart, it trav- left atrium pectinate cise. When the horse is at rest, its amount of air els through a network of arter- pulmonary muscle left atrium respiration rate is very low, with inspired, this ies, arterioles, capillaries, and trunk the animal sometimes taking 10 to condition venules. After completing that cranial 14 breaths or fewer per minute. also can part of the route in the equine vena cava However, when strenuous exercise result in body, it is returned to the heart is involved, the respiration rate increas- noisy air through large veins. es dramatically as the lungs move into The heart itself is divided into right high gear to satisfy the burgeoning two halves. Each of the halves ventricle coronary demand for oxygen throughout the of this large, muscular organ Air passes through the nostrils and left ventricle vessels body. There also is a pronounced along a lengthy nasal cavity, then it (3.3-8.8 pounds) has two cham- change in the effort involved. Respiratory System passes over the larynx and pharynx. bers—the atrium and ventricle. right atrium right atrium When the horse breathes while After passing through the trachea, the It works like this: The right atri- at rest, very little effort is re- inspired air arrives at the bronchial um and ventricle pump blood interventricular right ventricle chordaetendineae quired. However, when it trees within the lungs. gas exchange into the lungs, where it is loaded groove occurs in the alveoli, where the circula- left ventricle breathes rapidly to satisfy with oxygen. The oxygen-laden tory system receives oxygen and delivers the increasing demand for blood returns to the left side of it to tissues throughout the body, along interventricular septum oxygen, it is another matter. with nutrients absorbed from the digestive the heart, where the left atri- Now, the intercostal (situated Dr. roBin Peterson iLLustration system. um and ventricle then pump it

48 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 49 between the ribs) muscles and diaphragm oxygen—at least for a limited time—when intake, often referred to as “roaring.” The are called on to expand the chest, which, in the heart rate is 180 beats per minute or technical term is laryngeal hemiplegia (or turn, allows for expansion of the lungs. The less. When the heart rate is beyond that left laryngeal hemiplegia since it occurs base lung expansion allows for a greater quan- point, it is only a matter of time before the most often on the horse’s left side, the ex- trachea tity of air to be inspired. system will begin to falter. act cause for this is unknown). The amount of air inspired and expired There are many other problems that with each breath is called tidal volume. As Limiting Problems can affect the intake and exchange of air indicated, the number of breaths taken per Unfortunately, there are circumstances in the horse’s respiratory system. The bot- main alveolar minute is referred to as respiration rate or other than exercise that affect the amount tom line is that healthy lungs and airways bronchus sacs of the bronchial tree divide into smaller respiration frequency. Still another term of oxygen that can be utilized. are important, especially to the exercising and smaller bronchi. When cartilaginous involved is minute volume. Simply put, rAo One of the most troublesome con- horse. apex caudal plates are no longer present in the walls of this is the amount of air inspired and ex- ditions that affect respiration is recurrent lobe the smallest bronchi, the airway is termed pired in one minute. airway obstruction, or heaves, formerly Cardiovascular System apical lobe a bronchiole. The bronchioles, in turn, join The change in minute volume during known as chronic obstructive pulmonary We turn now to the cardiovascular or heart Dr. roBin Peterson iLLustration with the alveolar ducts that terminate in exercise can be dramatic. During rest, for disease (COPD). Basically, RAO is inflam- circulatory system of the horse. This con- the functional units of the lungs where gas example, the minute volume for a normal mation of the small bronchioles in the sists of blood, blood vessels through which exchange actually occurs—the alveoli. horse might be 150 liters per minute. Dur- lungs. When RAO strikes, the lower airway the blood flows, and the heart that provides The alveoli are small out-pouchings ing a fast gallop, this can quickly increase system is unable to function effectively. power for the flow of blood. throughout the body. increased, the horse’s heart rate goes up so along the walls of the alveolar sacs and al- to 1,500 liters per minute. Because minute The inflammation serves to develop ob- The normal adult horse weighing 1,000 Thus, it becomes obvious that the prime that more oxygen and nutrients can be de- veolar ducts. It is through the walls of these volume is a combination of respiration rate structions within the delicate airways and pounds will have about 13.2 gallons of function of the circulatory system is to livered to the tissues. The heart rate, quite tiny pouches that gas exchange takes place. and tidal volume, a horse can increase it air is unable to flow freely. As the condition blood in its body. The blood is composed deliver oxygen to tissues throughout the simply, is the number of times a horse’s The exchange occurs between air within al- either by breathing faster, breathing more worsens, more and more physical effort is of red blood cells (erythrocytes), white body, along with nutrients absorbed from heart beats during a minute. veoli and blood within the capillaries in the deeply, or both. involved when the horse inspires air. blood cells (leukocytes), platelets, and liq- the digestive system. It also acts as some- When a horse is at rest, his heart rate alveolar walls. However, there is a limit to the min- Recurrent airway obstruction can be uid (plasma). thing of a garbage disposal by delivering might be as low as 25 beats per minute. The alveoli have very thin walls between ute volume that can be achieved during caused by a number of conditions, with As indicated in the discussion on the the end products of cellular metabolism to When he is exercising at the maximal rate, oxygen-laden air in the lungs and the blood maximal exercise. When the horse is at a dusty hay and a dusty environment often respiratory system, the red blood cells the lungs and kidneys for removal. the heart rate can shoot as high as 250 vessels that contain red blood cells that will maximum exercise level—a heart rate that being implicated. have an iron-containing protein known The circulatory system also fills another, beats per minute. Obviously, the horse can carry oxygen to tissues throughout the body. has reached 200 beats per minute and be- eIPh Still another condition is known as hemoglobin, which binds oxygen for less spectacular role by helping to dissipate sustain this type of effort for only a short It is at this point that the two systems— yond—the blood leaving the lungs might as exercise-induced pulmonary hemor- transportation to the tissues. This is the heat by diverting blood toward the skin period of time. When the heart is beating respiratory and circulatory—join forces. not be carrying enough oxygen to ade- rhage (EIPH). Simply put, this condition primary function of the red blood cells. surface during exercise. at about 250 beats per minute, the cardiac The oxygen binds to hemoglobin for trans- quately service the tissues. This condition involves the presence of blood in the re- The main role for the white blood cells is Earlier, we pointed out that when exer- output is at the rate of approximately 55 port by the circulatory system to the tis- is referred to as arterial hypoxia. Generally spiratory tract during exercise. Horses to work with the rest of the immune sys- cise levels increase, so does the horse’s res- gallons of blood being pumped by the heart sues. speaking, the respiratory system can de- with this condition often are referred to tem to defend against bacterial invasions. piration rate. The same is true for the circu- per minute. The oxygen-laden red blood cells carry liver the re- as “bleeders.” The condition shows up in Platelets function in the blood clotting pro- latory system. As demands on the body are Another term utilized in discussions of their valuable product to the tissues, quired racehorses more than in any other disci- cess. where cell metabolism occurs and pline, although it can be found after any The key element in the en- coronary aortic valve CO2 is produced. The blood then strenuous exercise. tire vascular system, of course, EqUINE HEART groove heads back to the lungs via the roaring The larynx, which plays an im- is the heart, whose job it is to aorta pulmonary aorta pulmonary veins, but this time it is loaded portant role in the eating/breathing pro- pump blood through the cir- brachiocephalic veins cranial vena veins trunk cava with more CO2 than oxygen. cess, also can cause problems. In some culatory system. The flow of How much oxygen is taken in horses, the larynx does not open com- blood is through a system of and how much CO2 is expired pletely when the horse is breathing. blood vessels. When blood is depends on the amount of exer- In addition to limiting the pumped from the heart, it trav- left atrium pectinate cise. When the horse is at rest, its amount of air els through a network of arter- pulmonary muscle left atrium respiration rate is very low, with inspired, this ies, arterioles, capillaries, and trunk the animal sometimes taking 10 to condition venules. After completing that cranial 14 breaths or fewer per minute. also can part of the route in the equine vena cava However, when strenuous exercise result in body, it is returned to the heart is involved, the respiration rate increas- noisy air through large veins. es dramatically as the lungs move into The heart itself is divided into right high gear to satisfy the burgeoning two halves. Each of the halves ventricle coronary demand for oxygen throughout the of this large, muscular organ Air passes through the nostrils and left ventricle vessels body. There also is a pronounced along a lengthy nasal cavity, then it (3.3-8.8 pounds) has two cham- change in the effort involved. Respiratory System passes over the larynx and pharynx. bers—the atrium and ventricle. right atrium right atrium When the horse breathes while After passing through the trachea, the It works like this: The right atri- at rest, very little effort is re- inspired air arrives at the bronchial um and ventricle pump blood interventricular right ventricle chordaetendineae quired. However, when it trees within the lungs. gas exchange into the lungs, where it is loaded groove occurs in the alveoli, where the circula- left ventricle breathes rapidly to satisfy with oxygen. The oxygen-laden tory system receives oxygen and delivers the increasing demand for blood returns to the left side of it to tissues throughout the body, along interventricular septum oxygen, it is another matter. with nutrients absorbed from the digestive the heart, where the left atri- Now, the intercostal (situated Dr. roBin Peterson iLLustration system. um and ventricle then pump it

48 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 49 heart in a given time frame. horse can call on reserve red cell supplies The metabolic activity of the horse deter- to help meet demand. It also explains why mines blood flow. The higher the activity horses suffer less from altitude changes level, the higher the blood flow. The reason than humans. When a human goes from the heart rate increases with movement low to high altitude, a period of adjustment is that when a horse makes the transition is required. The horse simply releases more from rest to exercise, heavy demands are red blood cells from the spleen to satisfy baSiCS of life made on limb muscles as they increase lo- the increased demand for oxygen. By Les seLLnow comotion. This increased metabolic activ- As mentioned earlier, blood is also uti- the cardiovascular system is stroke volume. ity calls for increased blood flow, and the lized in the cooling process during exer- eproduction in all species borders on the miraculous. others involved in reproductive research, but much of the in- This is the amount of blood pumped with heart rate and stroke volume go up. cise. However, if the horse is exercising How else can one describe a process where two infini- formation utilized in this article emanated from those three each beat of the heart. When we multiply A unique aspect of the equine circulato- maximally for a long period of time, this Rtesimal entities, one from the male, the other from the institutions. heart rate by stroke volume, we come up ry system is that red blood cells are stored can result in a domino-effect series of female, join forces to produce living, breathing offspring? with another term—cardiac output. This is in the spleen and are released on demand. events. Reproductive capability or success varies by species. Mice The Mare the total amount of blood pumped by the This means during strenuous exercise, the As more and more of the blood is sent and rabbits, for example, are prolific producers of offspring. We’ll begin with the mare because her role in the repro- to the skin during the cooling process, de- Horses, on the other hand, fall into a category where it is ductive process is more complicated than that of the stallion. hydration becomes a factor as plasma is much more chancy. Basically, the mare serves four functions: lost in the process. Thus, it becomes some- When horses ran wild, this wasn’t a serious problem. There 1) She produces eggs or ova; thing of a catch-22. The blood helps cool were so many of them that their numbers continued to ex- 2) She provides housing and nourishment for the develop- the horse, but the loss of plasma through pand even though birth rate often was dictated by the avail- ing embryo, which becomes a fetus; Required Reading dehydration means that it is losing some ability of food and water. Once the horse was domesticated, 3) When the fetus reaches a certain state of maturity, the of the oxygen-carrying capacity to fuel tis- however, organized reproduction became the order of the mare expels it at the time of birth or parturition; and sues. day. Stables that depend on selling the offspring of stallions 4) The mare produces milk for nourishment of the young. for Responsible Horse Owners. and mares have an economic stake in breeding success. Yet, The mare’s reproductive tract lies in a horizontal position the process continues to be less than perfect, with success within the abdominal and pelvic cavities. The key elements When he is exer- rates hovering in the 65-70% range, and sometimes lower. are the vulva, vagina, cervix, ovaries, oviducts, and uterus. For over 10 years The Horse: Your Guide to Equine In this article on reproductive anatomy, we’ll take a look Vulva The vulva is the external opening of the reproductive at the reproductive organs of both the mare and the stallion tract. The labia are the lips of the vulva on each side of a five- Health Care has been essential reading by responsible cising at the maxi- and discuss just how they function in their effort to produce to six-inch vertical slit located below the anus. horse owners. mal rate, the heart another “miracle.” Once again, sources are too numerous to Vagina The vagina is comprised of a six- to eight-inch long Subscribe today, and along with your full access to rate can shoot as mention, other than to say that much of the basic informa- muscular tube lined with mucous membranes. It connects TheHorse.com, you’ll receive 12 issues of The Horse tion on reproduction available today stems from research at the vulva to the cervix. The tissues of the vagina are very high as 250 beats such institutions as Colorado State University, Texas A&M elastic so that it can accommodate the stallion’s penis during filled with essential information you need to know to University, and the University of Minnesota. There are many breeding and passage of the foal during the birthing process. keep your horses healthy and strong. Order now and per minute. SAVE OVER 72% off the cover price. Plus, you’ll get the next edition of The Horse Source FREE. As is the case with the respiratory sys- NO RISK. NO OBLIGATION. tem, a strong healthy circulatory system is Your satisfaction is absolutely guaranteed. If you’re needed if a horse is to remain healthy and not completely satisfied, we’ll send you a refund for all productive during serious exercise. A handy guide to unmailed issues! Take-Home Message the male and female While all the horse’s body systems work together to keep the animal alive and ac- reproductive tracts tive, the circulatory and respiratory systems have a special relationship. The flow SUBSCRIBE NOW! of blood and oxygen can make the difference between a champion and an ordi- CLICK HERE or nary horse, or when problems develop, it can mean the difference between life and call 1-800-582-5604 death. h

About the Author Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and he operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, includ- editor’s Note ing understanding equine Lameness, understanding the This is the final article in a 12-part series on equine young Horse, and the Journey of the western Horse, anatomy and physiology. If you missed any part of the published by Eclipse Press and available at www.Exclusively CQ06Z236TH series, be sure to look for the PDF version on TheHorse. Equine.com or by calling 800/582-5604. com in the coming months. Dr. roBin Peterson iLLustration

50 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 51 heart in a given time frame. horse can call on reserve red cell supplies The metabolic activity of the horse deter- to help meet demand. It also explains why mines blood flow. The higher the activity horses suffer less from altitude changes level, the higher the blood flow. The reason than humans. When a human goes from the heart rate increases with movement low to high altitude, a period of adjustment is that when a horse makes the transition is required. The horse simply releases more from rest to exercise, heavy demands are red blood cells from the spleen to satisfy baSiCS of life made on limb muscles as they increase lo- the increased demand for oxygen. By Les seLLnow comotion. This increased metabolic activ- As mentioned earlier, blood is also uti- the cardiovascular system is stroke volume. ity calls for increased blood flow, and the lized in the cooling process during exer- eproduction in all species borders on the miraculous. others involved in reproductive research, but much of the in- This is the amount of blood pumped with heart rate and stroke volume go up. cise. However, if the horse is exercising How else can one describe a process where two infini- formation utilized in this article emanated from those three each beat of the heart. When we multiply A unique aspect of the equine circulato- maximally for a long period of time, this Rtesimal entities, one from the male, the other from the institutions. heart rate by stroke volume, we come up ry system is that red blood cells are stored can result in a domino-effect series of female, join forces to produce living, breathing offspring? with another term—cardiac output. This is in the spleen and are released on demand. events. Reproductive capability or success varies by species. Mice The Mare the total amount of blood pumped by the This means during strenuous exercise, the As more and more of the blood is sent and rabbits, for example, are prolific producers of offspring. We’ll begin with the mare because her role in the repro- to the skin during the cooling process, de- Horses, on the other hand, fall into a category where it is ductive process is more complicated than that of the stallion. hydration becomes a factor as plasma is much more chancy. Basically, the mare serves four functions: lost in the process. Thus, it becomes some- When horses ran wild, this wasn’t a serious problem. There 1) She produces eggs or ova; thing of a catch-22. The blood helps cool were so many of them that their numbers continued to ex- 2) She provides housing and nourishment for the develop- the horse, but the loss of plasma through pand even though birth rate often was dictated by the avail- ing embryo, which becomes a fetus; Required Reading dehydration means that it is losing some ability of food and water. Once the horse was domesticated, 3) When the fetus reaches a certain state of maturity, the of the oxygen-carrying capacity to fuel tis- however, organized reproduction became the order of the mare expels it at the time of birth or parturition; and sues. day. Stables that depend on selling the offspring of stallions 4) The mare produces milk for nourishment of the young. for Responsible Horse Owners. and mares have an economic stake in breeding success. Yet, The mare’s reproductive tract lies in a horizontal position the process continues to be less than perfect, with success within the abdominal and pelvic cavities. The key elements When he is exer- rates hovering in the 65-70% range, and sometimes lower. are the vulva, vagina, cervix, ovaries, oviducts, and uterus. For over 10 years The Horse: Your Guide to Equine In this article on reproductive anatomy, we’ll take a look Vulva The vulva is the external opening of the reproductive at the reproductive organs of both the mare and the stallion tract. The labia are the lips of the vulva on each side of a five- Health Care has been essential reading by responsible cising at the maxi- and discuss just how they function in their effort to produce to six-inch vertical slit located below the anus. horse owners. mal rate, the heart another “miracle.” Once again, sources are too numerous to Vagina The vagina is comprised of a six- to eight-inch long Subscribe today, and along with your full access to rate can shoot as mention, other than to say that much of the basic informa- muscular tube lined with mucous membranes. It connects TheHorse.com, you’ll receive 12 issues of The Horse tion on reproduction available today stems from research at the vulva to the cervix. The tissues of the vagina are very high as 250 beats such institutions as Colorado State University, Texas A&M elastic so that it can accommodate the stallion’s penis during filled with essential information you need to know to University, and the University of Minnesota. There are many breeding and passage of the foal during the birthing process. keep your horses healthy and strong. Order now and per minute. SAVE OVER 72% off the cover price. Plus, you’ll get the next edition of The Horse Source FREE. As is the case with the respiratory sys- NO RISK. NO OBLIGATION. tem, a strong healthy circulatory system is Your satisfaction is absolutely guaranteed. If you’re needed if a horse is to remain healthy and not completely satisfied, we’ll send you a refund for all productive during serious exercise. A handy guide to unmailed issues! Take-Home Message the male and female While all the horse’s body systems work together to keep the animal alive and ac- reproductive tracts tive, the circulatory and respiratory systems have a special relationship. The flow SUBSCRIBE NOW! of blood and oxygen can make the difference between a champion and an ordi- CLICK HERE or nary horse, or when problems develop, it can mean the difference between life and call 1-800-582-5604 death. h

50 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 51 The middle is producing progesterone. With proges- increase about 50%. However, the glans layer is com- The Mare’s Reproductive Tract terone production shut down, the level of penis “flowers” or “bells” and increases in The Mare’s Reproductive Tract prised of mus- FSH will rise to the point where the whole size between 300-400% during erection. broad ligament of the uterus cular tissue cervix (behind vaginal cycle is started over again. The testicles are formed within the ab- uterine horns ureter right kidney and is called wall cutaway) What has been described above is the dominal cavity and, in the normal colt, oviduct oviduct the myome- anus way a healthy mare’s reproductive system descend into the scrotum between 30 trium. These normally functions when left to its own days before birth and 10 days after birth. uterine body rectum ovary muscles are design. However, it should be noted that The testicle is covered with a thick lay- ovary vulva Cervix The cervix provides entrance to responsible vagina some mares produce insufficient proges- er of connective tissue called the tunica right ovary infundibulum broad the uterus at the end of the vagina. The for pushing bladder terone, and that a wide variety of malfunc- albuginea. Fused to the outer surface of ligament cervix is about four inches long and forms the foal into fallopian tube tions can occur along the way. this capsule is the thin visceral vaginal tu- a boundary between the inside and outside the birth ca- nic. Supporting strands of connective tis- world with folded tissue. nal during The Stallion sue extend from the tunica albuginea to cervix When a mare is in estrus, the cervix is parturition. infundibulum The stallion’s prime function in the divide the testicles into lobules. vagina flaccid and open to facilitate the passage of The inner- reproductive process is two-fold: The non-capsular part of the testicle semen. When the mare is out of estrus, the most layer is 1) To produce the male reproductive is called the parenchyma. It consists of transverse fold eterson cervix is tightly closed and serves as a bar- the endome- cells known as sperm or spermato- seminiferous tubules (capable of produc- P in B o rier to prevent foreign agents from enter- trium, a com- zoa, as well as produce the male sex ing and conveying semen) and interstitial r vulva left uterine horn right uterine horn ing the uterus. plex mucosal hormone testosterone; and tissue situated between the seminiferous Dr. in Peterson B

ovary The primary sex organ of the membrane o 2) To introduce sperm into the female re- tubules. Located within the seminiferous r

mare is the ovary. She has two of these or- that contains Dr. productive tract at the proper time. tubules are Sertoli cells. They are involved Conclusive Act gans that are shaped somewhat like beans a rich blood The prime sex organs of the stallion are with the production of spermatozoa. In the We are now at a logical conclusion. The and are two to three inches in length. supply and many glands. It is the role of which stimulates sexual activity within the the testes or testicles, of which there are adult stallion, billions of spermatozoa are mare’s hormonal system has allowed her to The ovaries are located at the forward the uterus to house and nourish the devel- mare. It serves to prepare the reproductive two. Each testicle is suspended by the sper- produced daily in the convoluted seminif- be receptive to the stallion’s advance. The or upper end of the reproductive structure. oping fetus. tract and cervix for the arrival of sperm matic cord that extends from the abdomen erous tubules. After leaving the seminifer- cervix is open and relaxed. Ovulation is Their job is to produce eggs. When a female and causes the mare to be receptive to the to its attachment on the testicle. ous tubules, the spermatozoa travel to the on schedule. The stallion does his job and horse is born, her ovaries contain all of the The Role of Light stallion’s sexual advances. The testicles are normally ovoid (like an epididymis, which is lightly attached to the sperm is ejaculated. egg cells that her body will ever produce. A key element in the “miracle” of birth Luteinizing hormone facilitates matu- egg) and will measure 80 to 140 millimeters upper surface of each testicle. So, one might say, that for sure means a Each egg is contained in a little bubble-like is light. The mare’s reproductive activity is ration and ovulation of the growing, egg- in length and 50 to 80 millimeters in width. Located in the interstitial tissue between pregnancy. Not necessarily. There is a deli- container on the ovary called a follicle. seasonally polyestrous, which means that bearing follicle. Ovulation occurs when the Each will weigh about 225 grams. the seminiferous tubles are Leydig cells. cate time balance involved. The sperm cells Generally speaking, not much happens she has a reproductive season and a non- mature egg leaves the follicle and begins The testicles are housed in the scrotum, Their prime function involves the produc- live only 24 to 30 hours in the reproduc- with the follicles until the filly reaches reproductive season. Both are controlled its trip through the oviduct and into the which is an out-pouching of the skin. It tion of testosterone. tive tract of the mare. The timetable is even puberty. At that point, one or more of the by light. uterus. is comprised of two scrotal sacs—one for There are three basic processes involved tighter for the egg or ova. The egg remains follicles will begin to grow as the result of The non-reproductive season is known In the wake of ovulation, the estrogen each of the testicles—and it is separated by in the release of semen on the part of the viable for only four to six hours. an increase in fluid within the follicle. Nor- as anestrus and comes in the fall and win- level falls and the remains of the ovulated a septum. The scrotal sacs are located on stallion—erection, emission, and ejacula- Thus, one can say, when pregnancy, fol- mally, if nature is left to its own design, the ter when there is little light. The reproduc- follicle are converted to form a corpus lu- either side and in back of the penis. tion. Erection has been discussed. Emission lowed by birth of a live foal, does occur, it rest of the follicles will remain small and tive season begins in the spring when days teum (CL) or yellow body (a temporary The penis is the male organ of copulation is the movement and deposition of sperm is indeed a “miracle.” H quiescent until it is their turn. are longer, and it lasts into the summer. glandular mass). Granulosa cells in the CL and is comprised of three parts—the root, and fluid from the deferent duct and tail of About the Author oviducts When the egg reaches a par- However, the seasons are not all that cut secrete the hormone progesterone. Its job which attaches the penis to the pelvis via the epididymis as well as fluids from the ac- Les Sellnow is a free-lance writer based near Riverton, ticular point of maturity, the follicle and dried. In between those two basic sea- is to shut down the secretion of the estrus- two strong ligaments and a pair of muscles; cessory sex glands, into the pelvic urethra. Wyo. He specializes in articles on equine research, and he ruptures and the egg is discharged. The sons are two other cycles, known as tran- stimulating hormones and set the stage for the body or shaft, which is the main portion Ejaculation is the actual expulsion of the operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, includ- egg is then trapped in the infundibulum, a sitional stages. One occurs just before the maintenance of a pregnancy. of the penis; and the glans penis, which is semen out through the urethra. In the stal- ing understanding equine Lameness, understanding the funnel-shaped membrane that surrounds mare becomes reproductively active and As progesterone carries out its tasks, the the enlarged front end of the penis. lion, ejaculation occurs as a series of strong young Horse, and the Journey of the western Horse, the ovary. the other occurs just prior to anestrus. Dur- cervix closes, contractions along the repro- The major portion of the penis is formed pulsing contractions so that several succes- published by Eclipse Press and available at www.Exclusively Equine.com or by calling 800/582-5604. The infundibulum narrows and becomes ing these two periods, mares generally are ductive tract cease, and the mare loses all by the corpus cavernosa (a pair of sponge- sive “jets” of semen are spurted forth. a coiled tube known as the oviduct. The erratic in their cyclic and sexual behavior. interest in the stallion’s advances. like columns of erectile tissue that becomes oviduct connects to the uterus and carries Light jump-starts the reproductive sys- What happens next is dependent on engorged with blood during erection). The Stallion’s Reproductive Anatomy the egg to that location in the wake of fer- tem by stimulating the hypothalamus whether the mare became pregnant. If she The corpus spongiosum is a small area tilization. gland located within tissues at mid-brain to did, progesterone will continue to function of spongy erectile tissue that immediately Uterus The uterus is the largest of the fe- produce gonadotropin-releasing hormone in its role of maintaining the pregnancy by surrounds the urethra. It also becomes male reproductive organs and is capable of (GnRH). When enough GnRH is produced, suppressing other hormonal activity. engorged with blood during erection. The expansion as the fetus grows and develops. the pituitary gland at the base of the brain is However, if the mare does not become glans penis is filled with a multitude of preputial ring The uterus is multi-layered, hollow, and Y- stimulated. The pituitary then secretes two pregnant, changes will take place to pre- nerve endings and becomes engorged and shaped. The base of the Y is the uterine hormones—follicle stimulating hormone pare the way for another try at pregnancy. erect during sexual excitement. body, while the two branches are known (FSH) and luteinizing hormone (LH)—that The uterus will remain under the influence When not erect, the stallion’s penis is ap- glans penis inner lamina of arner

as horns. Two tough, sheet-like structures, act on the ovaries. Follicle stimulating hor- of progesterone for 12 to 14 days, but after proximately 50 centimeters in length and V prepuce scrotum containing known as broad ligaments, suspend the mone moves via the bloodstream to the that the uterus reacts. 2.5 to five centimeters in diameter. The pe- testes kson C i uterus within the body cavity. There are ovaries, where it stimulates the production If the mare is not pregnant at that stage, nis is contained within the sheath or pre- D r. three distinct layers in the uterus. The out- of one or more follicles. the uterine endometrium will secrete the puce, which forms two folds around the D free body of penis ermost is continuous with the broad liga- When the follicles reach 20 to 25 milli- hormone prostaglandin. The first thing free end of the penis. urethral process ments and is known as the serous layer. meters in diameter, they secrete estrogen, prostaglandin will do is destroy CL that During erection, the size of the penis will Courtesy

52 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 53 The middle is producing progesterone. With proges- increase about 50%. However, the glans layer is com- The Mare’s Reproductive Tract terone production shut down, the level of penis “flowers” or “bells” and increases in The Mare’s Reproductive Tract prised of mus- FSH will rise to the point where the whole size between 300-400% during erection. broad ligament of the uterus cular tissue cervix (behind vaginal cycle is started over again. The testicles are formed within the ab- uterine horns ureter right kidney and is called wall cutaway) What has been described above is the dominal cavity and, in the normal colt, oviduct oviduct the myome- anus way a healthy mare’s reproductive system descend into the scrotum between 30 trium. These normally functions when left to its own days before birth and 10 days after birth. uterine body rectum ovary muscles are design. However, it should be noted that The testicle is covered with a thick lay- ovary vulva Cervix The cervix provides entrance to responsible vagina some mares produce insufficient proges- er of connective tissue called the tunica right ovary infundibulum broad the uterus at the end of the vagina. The for pushing bladder terone, and that a wide variety of malfunc- albuginea. Fused to the outer surface of ligament cervix is about four inches long and forms the foal into fallopian tube tions can occur along the way. this capsule is the thin visceral vaginal tu- a boundary between the inside and outside the birth ca- nic. Supporting strands of connective tis- world with folded tissue. nal during The Stallion sue extend from the tunica albuginea to cervix When a mare is in estrus, the cervix is parturition. infundibulum The stallion’s prime function in the divide the testicles into lobules. vagina flaccid and open to facilitate the passage of The inner- reproductive process is two-fold: The non-capsular part of the testicle semen. When the mare is out of estrus, the most layer is 1) To produce the male reproductive is called the parenchyma. It consists of transverse fold eterson cervix is tightly closed and serves as a bar- the endome- cells known as sperm or spermato- seminiferous tubules (capable of produc- P in B o rier to prevent foreign agents from enter- trium, a com- zoa, as well as produce the male sex ing and conveying semen) and interstitial r vulva left uterine horn right uterine horn ing the uterus. plex mucosal hormone testosterone; and tissue situated between the seminiferous Dr. in Peterson B ovary The primary sex organ of the membrane o 2) To introduce sperm into the female re- tubules. Located within the seminiferous r

52 www.TheHorse.com The horse December 2006 December 2006 The horse www.TheHorse.com 53 061019 OCD ad w stuart.qxp 10/18/2006 3:18 PM Page 1

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