FORM AND FUNCTION

Conformation of the : Relationship of Form to Function

G. Marvin Beeman, MS, DVM

A thorough understanding of the conformation of the horse is fundamental to the approach of assessing musculoskeletal issues; being the most significant; however, this information is also valuable in assessing the medical status of a horse for purchase, for selecting sires and dams for breeding and shoeing recommendations. A systematic approach to evaluating conformation will enhance the ability of the practitioner to determine defects in a rapid manner and avoid overlooking those issues that can contribute to current problems or predispose to problems in the future. Au- thor’s address: Littleton Large Animal Clinic, 8025 South Santa Fe Drive, Littleton, CO 80120; e-mail: [email protected]. © 2008 AAEP.

1. Introduction The third and most significant definition is the The purpose of this presentation is to provide: “relationship of form and function.” This is the way (1) an overview of the conformation of the horse, (2) that the horse’s structure allows it to perform its an approach to the evaluation of conformation, (3) method of ambulation either on its own or while an evaluation of the effect that conformation has on working or performing for man. To better under- the dynamics of equine locomotion, and (4) the cor- stand the conformation relationship of form to func- tion, a standard of excellence of a horse should be relation of defects in conformation that contribute to established that considers the dynamics of locomo- pathology in the horse. tion coupled with soundness or lack thereof. In this The definition of conformation can be articulated discussion, the word “sound” is interpreted as being in different ways. Webster’s Dictionary simply de- free of infirmities, usually lameness. In reality, the fines it as the “form or outline of an animal.” This word “sound” means free of the “seeds” of disease, can be applied to the standard diagrams of a horse but obviously, this is next to impossible for any from a lateral, cranial, and plantar view with plumb horse. lines applied. This procedure establishes a basic For years, much of a horse’s success or failure has visual means to determine if the limbs are straight been attributed to its conformation. There are and the angles are correct. sketches and descriptions of Alexander the Great’s Another definition of conformation is “the sym- horse Bucephalus (356–323 BC). The De re eques- metrical arrangements of its parts.” This encom- tri by the Greek historian and philosopher Xeno- passes the horseman’s perception of the “well-made” phon (430–354 BC) goes into detail about good and horse. Those parameters are often described as bad conformation. An Essay on the Proportions of beauty, balance, and symmetry. Eclipse by Charles Vial de Sainbel1 and The Exterior

NOTES

AAEP PROCEEDINGS ր Vol. 54 ր 2008 1 FORM AND FUNCTION of the Horse by Armand Goubaux and Gustave Bar- variables. The distance is measured to the inch, rier2 are extensive descriptions of the horse. There the surface is relatively the same, the direction is have been significant scientific works relevant to the same, the weight of the load is the same, and the conformation from the time of Goubaux and Barrier tack is very similar. Consequently, when a horse to the present.3,4 from this testing ground is the best, it should be Conformation is not the only factor responsible for studied carefully for its conformation attributes. a horse’s ability to perform the tasks man asks of However, this logic would cause the student of con- him. Certainly, there are other intrinsic factors of formation to interpret that speed is the best evalu- the horse that obviously contribute to their athletic ation of conformation.6 This logic does not hold ability, such as the cardiovascular, respiratory, ner- true because speed and bad conformation equal a vous, and digestive systems. The horse’s unique short-term racehorse. The best combination is quality to give maximum effort when asked is best good conformation, speed, and “heart.” A visualiza- referred to as “heart.” In addition, there are nu- tion of this method of assessment of conformation merous extrinsic factors that affect a horse’s perfor- can be seen in “The Perfect Horse” by noted equine mance such as the degree of training, physical artist Richard Stone Reeves; in this work; the artist fitness, state of health, shoeing, tack used, and cer- used Tie Polleto’s head and neck, Citation’s shoul- tainly, the rider. der, Jay Trump’s forelegs, Vaguely Nobel’s middle Before exploring the depths of conformation, the piece, Buck Passer’s quarters and hindlimbs, and type of horse needs to be put in the correct context. Graustark’s color. In his description of “The Per- Type is defined as the inherited characteristics of an fect Horse,” he stated that “all the were top animal that fit it for a certain use.5 The Thorough- class runners indeed; there is hardly a top class bred type is suited to running. The American runner in existence with faulty conformation.” Quarter Horse type is designed to perform activities Another apropos statement is by W. J. Miles: that require quick speed and muscle mass. The “Who’er expects a perfect ‘horse’ to see expects what Arabian type is suited to travel great distances with never was, or is, or e’er shall be.”7 James Rooney, the least amount of expended energy. In an evalu- VMD, made a very correct statement: “Even near ation of the horse’s conformation relevant to the perfect conformation will not protect a horse from type, it becomes obvious that one horse cannot do all lameness if the external force departs too far from the tasks that man asks of them. The difference in the normal range. Conversely, even a slight horse types is exemplified by the extremes of the change in the external force can cause lameness if and the large . Correct the conformation is too bad.”6 conformation is fundamental in any type of horse. In the assessment of a horse’s conformation and 3. Factor II: Dynamics of Locomotion the relationship of form to function, a standard of I believe the horse is one of, it not the best, mam- excellence must be established. Additionally, the malian athlete that God has created. Granted, dynamics of locomotion must be understood, and a they cannot run as fast as a cheetah or jump as high correlation to soundness must be made. A stan- as many of the deer species; however, none of those dard of excellence is established by those horses that animals run or jump with the weight of a rider on excel in the dynamics of locomotion to accomplish their , which often approaches 15–25% of the the tasks asked of them and in doing so, remain horse’s body weight and can be 2–3 ft above the relatively free of unsoundness. horse’s center of gravity. The gaits of the horse 2. Factor I: Standard of Excellence contribute to their dynamics of locomotion, and con- formation is basic as to how the horse ambulates. This will vary with the purpose of the horses. The The dynamics of locomotion are the result of syn- Arabian, the Morgan, and horses of this type are chronization of the actions of the horse’s biological designed for excellence of movement of gait; this is systems. The skeleton is the key to a horse’s in contrast to the and the method of progression and the foundation of its who are designed for excellence of conformation. speed of gait.5 Multiple subtle conformation dif- ferences are apparent in these examples of stan- dards of excellence. The head and neck position, 4. Factor III: Soundness the angle of the shoulder, and the angle of the croup Unsoundness is defined as that system or structure are three of the most significant factors that sepa- that is not sound, not working, or painful. Muscu- rate the standards. In fact, these factors also assist loskeletal system infirmities are the most common in defining the type of horse. Horses given a gen- infirmities that veterinarians encounter; however, eral objective established a standard. One of the defects in the respiratory, cardiovascular, digestive, purest modalities to establish a standard is through and nervous system also alter the horse’s dynamics the trial by peers. Flat racing has to be one of the of locomotion. Most lameness is the direct effect of best environments to facilitate trial by peer. It has stress, strain, and concussion on the musculoskele- the least influence by man’s judged opinions, be- tal system; therefore, conformation defects that en- cause the proving grounds have the most constant of hance these forces are the most significant and

2 2008 ր Vol. 54 ր AAEP PROCEEDINGS FORM AND FUNCTION provide a basis to establish what value should be sides of the same coin. If a structure does not tell assigned to the various conformation defects. us about function it means we have not looked at it Unsoundness, most often lameness, usually deter- correctly.”a This statement adds succinct evidence mines a horse’s useful lifetime. Therefore, confor- as to why conformation of the horse should be eval- mation becomes the common denominator to the uated as it relates to the function. horse’s ability to perform and stay sound. Conformation defects distract from the standard The correlation of the three factors (standard of of excellence, limit the dynamics of equine locomo- excellence, dynamics of locomotion, and soundness) tion, and predispose the horse to unsoundness. provides a method to better understand the meaning Most often, there is a combination of defects present of the conformation relationship of form to function. in a horse that can be considered to be contributing A method of assessing “balance” has been well illus- to the lameness. There has been considerable lit- trated by Gladys Brown Edwards.8 Synonymous erature produced that relates conformation defects with balance is the center of gravity of the horse as to unsoundness. Most of the opinions expressed has been defined by many authors.2,5,9–11 The lo- are based on experience and qualitative observa- cation of the center of gravity is helpful in under- tions rather than scientific fact; recently, however, standing why 60–65% of the horse’s body weight is more quantitative and/or analytical work has been born by the forelimbs. This fact explains why the done.3 As a result of the recent research using front limbs are the sight of the majority of lameness. modern technology, the empirical observations may The evaluation of conformation has been and is or may not be proven. Until that happens, we must currently subjective; however, more and more objec- press on with what we have perceived to be correct tive evaluations of conformation are being developed from evidence-based medicine. An example of evi- with the advent of sophisticated research enhanced dence-based medicine showing significant issues is by the application of modalities. These modalities the case of a field hunter that had a combination of provide specific information as to the movement of conformation defects; when he was subjected to con- the horse and define the effects of conformation on siderable stress, strain, and concussion, he became the movement of specific parts of the horse. Then, unusable from the infirmities that developed. In this information can be used to evaluate the alter- addition, a critical review of his history as a field ation in performance and to understand the delete- hunter revealed several deficits in his function that rious effects on the musculoskeletal system.4 could be attributed to his conformation faults. The As is the case with evaluating a horse for infirmi- horse was closely observed from birth to his nec- ties, a methodical, thorough system is the most pro- ropsy by the author. ductive method to assess a horse’s conformation. The conformation of the foot is critical. The To avoid overlooking important factors, the exam “mouth of the funnel” is where all of the concussive should be divided into five categories. force is transmitted to the external surface. The foot can be variable in shape and size depending on 1. Head, neck, body, and balance many factors such as breed, type, specific use, and 2. Forelimb (from the top of the scapula to the even geography; however, Goubaux and Barrier2 bottom of the foot) stated that, in all cases, the foot should be propor- 3. Hindlimb (from the top of the croup to the tional to the height of the horse, his weight, his bottom of the foot) confirmation, and his special aptitudes. It be- 4. Type hooves the veterinarian to be very aware of the 5. Way of going specific anatomical structures, especially those structures that are so critical for the support of the The need for equine practitioners to have an appre- tremendous amount of force that is generated at the ciation of a horse’s conformation was very well said hoof-ground interaction. Asymmetrical feet are a by R. H. Smythe, MRCVS in Equine Medicine and conformational defect of significance. In the au- Surgery: “When those involved with the welfare of thor’s experience, uneven feet (especially front feet) the horse possess some knowledge of conformation are an issue of consequence in that Ͼ60% of the and its relationship to the dynamics of equine loco- lameness encountered in the foot will be in the one motion they can better derive ways of lessening the that has a smaller frog, more vertical bars, enlarged effects of injurious factors and they can better prog- heels above the coronet band, and a greater distance nosticate the extent of the resulting lameness.”12 from the bearing surface of the heel to the coronet This statement very well explains the veterinarian’s band. “No frog, no foot; no foot, no horse” by role in understanding the conformation of the horse; Lafosse13 is still as important today as it was several not only will this add to the veterinarian’s ability to hundred years ago. The dorsal surface of the hoof manage lameness, it will assist them in dealing with wall and the dorsal surface of the should be their clientele on horse shoeing issues, purchase parallel. These angles vary a great deal from horse examinations, and selection of breeding animals. to horse. The angle of the foot and pastern has a Bacteriologist Szent-Gyorgyi in 1950 said when physical effect on the angle of the fetlock, which is describing a single cell that “there is no real differ- the major site of the change of direction and absorp- ence between structure and function; they are two tion of the force being directed down the limb.

AAEP PROCEEDINGS ր Vol. 54 ր 2008 3 FORM AND FUNCTION Therefore, a short upright pastern is believed to In viewing the forelimbs from the front, the plumb increase the concussion on the fetlock, the phalan- line from the middle of the scapula humeral joint to geal joints, and the foot. A long, sloping pastern the ground establishes the correct alignment of the will generate excessive hyperextension of the fet- forelimb. It should bisect the column of bone includ- lock, which puts strain on the suspensory apparatus ing the foot from the elbow to the ground. Common of the limb. A broken angle of the pastern also defects are in at the knees, toe out, base narrow toe in, generates excessive strain on the phalangeal joints base narrow, base wide, off-set knees, bench knees, and supporting soft tissue structures. The fetlock and pigeon toed. should be sufficient in size to absorb and change the The plumb line application for the hindlimb has a direction of the forces being directed down the limb. similar application. From the lateral, the line view The plumb line concept is very useful in under- dropped from the tuber ischii should touch the point standing deviation of the limbs that is considered to of the hock and continue touching the leg along the be detrimental to the horse’s ability to perform and plantar surface to the fetlock. Deviations from the remain free of unsoundness. The basic premise is normal are sickle hocks, camped out behind, and that strain and concussion will be concentrated post legged. The hock is the major articulation for where there is a change of direction in the plumb the dramatic flexion of the hindlimb that is neces- line stress. The line dropped from the tuber of the sary to advance the limb; however, the post-legged spine of the scapula should bisect the column of limb defect also involves the femero tibial articulation. to the fetlock and fall just behind the heel. The The hock is the most common site of hindlimb lame- defects of the forelimb that are noted from the lat- ness, but the stifle is becoming more and more of an eral view above the fetlock and pastern are over at issue because of the straighter hindlimb in many of the knee, back at the knee, camped under, camped the larger breeds. out, and tied in below the knee. It becomes obvious The plumb line application from the rear on the that the carpus conformation is critical because it is plantar view is from the tuber ischii bisecting the the major joint that virtually makes the forelimb hindlimb to the ground. The deviations of signifi- function like a spoke of a wheel when the limb is full cance are cow hocks, base narrow, and base wide. weight bearing. Then, when the breakover portion Note that a cow-hocked problem is present when the points of the hock are closer together than the fet- of the stride is activated, it becomes the major flexor locks. Hindlimbs can toe out and not be cow joint of the forelimb. Therefore, the carpus must be hocked. large, facing squarely rostral, and positioned medi- Conformation defects in the rear fetlock, pastern, ally and laterally equidistant between the radius or foot are similar to those in the forelimb; however, and the third metacarpal bone. The third metacar- they are more tolerable because less weight is placed pal bone should be relatively short in relationship to on them than the forelimb. the length of the radius because of the mechanical The conformation of the head contributes signifi- advantage that this creates. It functions as a lever cantly to the function of the horse. In addition, it is for the muscles and tendons of the forelimb to position one of the hallmarks of the horse’s beauty. Several the foot in the most optimum position. It also has to points contribute to both the beauty and function. be sufficient in size to withstand the forces on it. The length of the head needs to be only large enough The radius is the site of the majority of the mus- to provide space for the teeth, to allow room for the cles that flex and extend the lower limb. Therefore, turbinates to temper the air going to the lungs, and the longer that it is relevant to the metacarpus to catch debris. Large nares are essential to permit makes the lever action more efficient. The olecra- maximum air intake. Excessive length and depth non and the olecranon fossa of the humerus is vital only adds excessive weight to the “balance ball” on to the fixing of the lower limb to act as a “spoke of the the end of the balance arm (the neck). Large eyes wheel.” Therefore, the length of the humerus is located at the edge of the forehead enhance the arc of vital to position the spoke of the wheel very near to vision. A clean throat latch along with significant a vertical line below the center of gravity of the width between the mandibulii is important. All of horse. The length of the humerus is difficult to this makes sense because everything that makes a visually evaluate, but it is a very important horse function passes through the throat latch area: structure. air, food, blood to the brain, and the spinal cord. The scapula and scapulo humeral joint need to be A long neck enhances the horse’s ability to adjust its evaluated together. It should be noted that there is balance and reduce weight on the forelimbs. The very little articular movement in the scapulo hu- withers are very important if horses are to be ridden meral joint, even at speed. The significant function to help keep the off of the top of the scapula is two-fold; the scapula rotates around a point in its and in the middle of the back without excessive middle, and it glides back and forth on the rib cage. pressure from the girth (cinch) on the rib cage. Therefore, three factors are important in evaluating The back (thoracic and lumbar vertebral column) the conformation of the “shoulder”: (1) angle, (2) should be flat to be the most efficient to support the length, and (3) positioning of the attachment to the large mass of the viscera and a rider. Also, it is the rib cage. lever that facilitates the elevation of the forelimbs,

4 2008 ր Vol. 54 ր AAEP PROCEEDINGS FORM AND FUNCTION head, and neck, which is critical to horse’s various They should be based on a standard of excellence, functions. The croup (sacral vertebra) should be the dynamics of locomotion, and soundness. long whether or not it is sloping or flat (the Arabian References and Footnote versus the Quarter Horse). The heart girth (rib 1. Vial de Sainbel C. Essay on the proportions of eclipse. cage) should be deep, because it provides the frame- Wright J, London; 1795. work to house the viscera. 2. Goubaux A, Barrier G. The exterior of the horse, 2nd ed. Confirmation is inherited—good and bad. There Philadelphia: J.B. Lippincott, Harger S, ed. Ch 11, Center of seems to be a difference of opinion as to the value of gravity; 3-11 1982;1–20. 3. Crevier-Denoix N, van Weeren PR. Equine conformation: the heritability. Science will hopefully provide a Clues to performance and soundness? Equine Vet J 2006; better answer in the future. 38:591–596. In summary, the evaluation of the conformation of 4. Rossdale RD, Butterfield RM. Conformation: a step along the horse continues to be based on age-old empirical the pathology to objective assessment. Equine Vet J 2006; practices. However, research is providing the 38:588–590. 5. Beeman GM. Correlation of defects in conformation to pa- equine practitioner with more sound data to either thology in the horse, in Proceedings. 29th Annual American support or refute concepts that have evolved Association of Equine Practitioners Convention 1983;177. through years of acute observation and the correla- 6. Adams OR. Lameness in horses, 1st ed. Philadelphia: tion of good and bad qualities that affected a horse’s Leo and Febiger, 1962. 7. Miles WJ. Modern Practical Farriery, London. The Gresham ability to perform or caused musculoskeletal infir- Publishing Company, 1877. mities. The breeding of the horse provides the ge- 8. Edwards G. Anatomy and conformation of the horse. The netic background in attempting to predict the Thoroughbred of California. 42(6)1-4. potential ability. After that, conformation becomes 9. Rooney JR. Biomechanics of lameness in horses. Balti- more, Maryland: The Williams and Wilkins Co., 1969. the deciding factor as to whether or not an individ- 10. Adams OR. Lameness in horses, 2nd ed. Philadelphia: ual may be used for a specific function. It would be Leo and Febiger, 1993. simpler if the only necessary criteria were those 11. Stashak TS, Hill C. Conformation and movement. In: stated by the famous Italian horse breeder Federico Stashak TS, et al. Adam’s lameness in horses. Philadelphia: Leo and Febiger, 2002;73–98. Tesio who said that a “horse gallops with his lungs, 12. Smythe RH. Equine Medicine and Surgery. American Ver- perseveres with his heart and wins with his terinary publication. Santa Barbara, CA 1963. character.”14 13. Lafosse EG. Observations and discoveries made upon horses Until such time that it is proven otherwise, the with methods of shoeing. Nourse J, London; 1994. root of studying conformation should include those 14. Tesio F. Breeding the racehorse. Allen JA, London; 1994. factors that relate the horse’s form to its function. aLo¨rinez A. Personal communication.

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