Practical Understanding of Claw Lesions Sarel Van Amstel, BVSc, College of Veterinary Medicine University of Tennessee, Knoxville, TN Introduction Successful control and and swelling resulting in more pain and management of lameness in commercial inflammation. Progression from partial to swine operations should include the full thickness horn lesions develops over following: Early detection of lameness time but is also dependant on other problems on an individual and herd factors such as flooring and housing. basis. This can be achieved by: 1) Close Hard floors increase concussion on observation of individual animals for individual claws and dissipation of signs of lameness and/or lesions (See tension forces through the claw created flow chart); 2) Lesion identification and by weight bearing becomes less record keeping; 3) Knowledge of the efficient. This may not only lead to causes and corrective actions progression of existing lesions but can necessary for each of the different lead to mechanical trauma of the soft lesions. tissues within the claw which will result in further pain and inflammation. This Visible lesions of the foot without applies particularly to the outer claw of swelling or lameness do not penetrate the back leg which carries more weight through the full thickness of the horn compared to the inner claw. Overgrowth (wall, sole, heel or white line) and as a of the outer claw may further predispose result cause no pain and require no the claw to mechanical trauma. In immediate action. However, it is unpigmented claws inflammatory important that lesions are identified and changes can be seen as red the prevalence recorded. High discoloration below the horn surface. prevalence rates warrant investigation Swelling at and above the coronary as to the possible cause in order to band, particularly in the presence of a institute corrective actions. For example, discharging tract, are signs of deep vertical wall cracks may indicate poor sepsis of the foot often accompanied by horn quality and keratinization and may osteomyelitis. Such lesions are serious point to nutritional imbalances or and usually unresponsive to treatment. deficiencies. Lesions that penetrate though the full thickness of the horn Lameness in the absence of visible cause pain due to penetration into the lesions may indicate problems in the corium (the underlying soft tissue layer) upper leg such as osteochondrosis or which is highly innervated with pain osteoarthritis. Osteoarthritis may follow receptors. Trauma and infection of the osteochondrosis and is commonly seen exposed corium lead to inflammation in the elbow joint of older pigs. FeetFirst® Sow Lameness Symposium II, Minneapolis, Minnesota, USA, August 31-September 2, 2010 41 Structure of the foot The foot includes the limb below the distal interphalangeal (DIP). P3 is fetlock joint. It is comprised of two digits completely enclosed within the claw each of which has a horn-covered claw. horn capsule.The deep flexor tendon is The term “claw” is preferable to hoof. attached to the flexor tuberosity at the When referring to an area nearest the back P3.The navicular bone is attached longitudinal axis (i.e. toward the center) to P3 and also to P2. The navicular bursa it is designated as axial, whereas is situated between the navicular bone structures away from the center are and the deep flexor tendon and permits designated as abaxial. movement of the deep flexor tendon over the surface of the navicular bone Each digit of the foot consists of: during extension and flexion of the claw. phalanx 1 (P1), phalanx 2 (P2), phalanx P3, the DIP joint, navicular bone and 3 (P3), and navicular bone; and 2 joints: navicular bursa are within the claw horn proximal interphalangeal (PIP) and capsule. The claws The purpose of the claw horn parallel to each other. Toward the heel capsule is to protect the underlying these ridges diverge reflecting a more sensitive tissues of the corium and rapid rate of growth in the heel region dissipate the concussion forces that due to faster rates of wear. In mature occur when the digits impact the ground. sows the normal toe length is 45 to It consists of the wall, which can be 50mm. divided into the abaxial (outside) and the axial (inside). The abaxial wall is further The sole is connected to the wall subdivided into the dorsal (or front/toe) by means of the white line. The white and lateral (abaxial) aspects. The wall line courses forward from the area of the is demarcated from the heel on the heel on the abaxial side of the claw, abaxial side of the claw by the abaxial around the tip of the toe and about 1/3 groove. Perioplic horn is the softer horn of the way back on the axial side of the lying just below the skin-horn junction. claw’s weight bearing surface. The white At the back of the foot the periople line is a unique and important structure. gradually widens and eventually It is the softest horn within the claw becomes the horn of the heel. Coronary capsule. This permits it to provide a horn, the hardest horn within the claw flexible junction between the harder capsule makes up the bulk of the horn horn of the wall and the softer horn of of the wall. The wall has faint ridges or the sole. On the other hand, because of rugae, which run horizontally and its softer nature it also represents a FeetFirst® Sow Lameness Symposium II, Minneapolis, Minnesota, USA, August 31-September 2, 2010 42 weak area on the weight-bearing tubules per mm2 in the wall and 20/mm2 surface that is vulnerable to damage. in the sole and heel. Intertubular horn The epidermal layer overlying the interconnects the tubular horn. corium produces horn cells in the form Intertubular horn consists of sheets of of tubules (tubular horn). Cells within the elongated horn cells arranged parallel tubules are arranged in a steep spiral with the bearing surface. Since tubular around the center axis. Tubules differ in horn is what imparts structural strength size, number and shape in various parts to the horn capsule, it follows that the of the claw and are round near the horn of the wall is structurally the inside of the wall and oval near the strongest followed by the sole and the surface. There are approximately 80 heel. Horn quality and physical properties Horn quality is dependent on a of protein, energy, lipids, vitamins A, D number of internal as well as external and E, calcium and phosphorous. factors. Internal factors would include Micronutrients such as the sulfur blood and nutrient supply whereas containing amino acids like cysteine and external factors relate to environmental methionine are essential for cross- influences. Horn production requires linking of keratin filaments. Trace good vascular supply. Any compromise minerals particularly zinc, copper and in blood flow will have a negative effect the vitamin biotin have very important on horn production. Horn production is roles in the keratinization of horn cells also dependent on the supply of and integrity of the intercellular nutrients which include adequate levels cementing substance of claw horn. Biomechanics of weight bearing Observation of slaughter house heel of the outer claw overgrows and as specimens and claw measurements such is more predisposed to mechanical have shown that weight bearing injury particularly on hard walking between front claws is relatively evenly surfaces. In some instances it appears distributed while there is a significant as if the inner claw of the back leg is difference in claw size between the almost non-weight bearing and under- outer and inner claws of the back leg. goes disuse atrophy. A genetic base for The outer claw has a larger surface area this difference in claw size needs to be and carries more weight. As a result the investigated. FeetFirst® Sow Lameness Symposium II, Minneapolis, Minnesota, USA, August 31-September 2, 2010 43 Pathogenesis of lameness Lameness is an indication of the steroid (cortisol) release results in presence of pain. The corium is highly gluconeogenesis (break down of body innervated with pain nerve endings. protein to glucose), and activates Inflammatory changes cause the hormone sensitive lipase, an enzyme release of cytokines and which converts body fat (triglycerides) to neurotransmitters which activates pain fatty acids for transport to the liver fibers resulting in transmission of pain where it is used for energy. Cortisol also signals to the brain. Pain is highly causes insulin resistance which makes it catabolic and results in significant more difficult for blood glucose to enter weight loss despite maintenance of cells which in turn will induce further normal food intake. The basal cellular breakdown of body reserves. metabolic rate is elevated. Endogenous Horn lesions The claw consists of structurally Sole: Fissures/cracks and sole crack different types of horn which on at the heel/sole junction biometric strength (hardness) ranks as Heel: Erosion and cracks follows (hard to most soft): wall; sole; Coronary band: Hemorrhage; heel; coronary band and white line. discharging tract and swelling Lesions in the different areas are the White line: Hemorrhage; separation following: which is often continuous with Wall: Horizontal and vertical wall separation at the wall/heel junction fissures; Wall crack at the wall/heel and/or heel/sole junction. junction; wall hemorrhages; overgrowth Vertical wall fissures Vertical wall fissures occur mainly on Intercellular cementing substance the abaxial wall in one or multiple claws. consists of long chain fatty acids. Biotin The fissure may start at the coronary is important in the production and band or the bearing surface and may elongation of these fatty acids and involve part or full length of the wall. supplementation of biotin can reduce Cracks start in the intertubular horn and the prevalence of vertical cracks in progress along the intercellular cement problem herds.