Laminitis is a disease that affects the feet of ungulates and is found mostly in horses and cattle. Clinical signs include foot tenderness progressing to inability to walk, increased digital pulses, and increased temperature in the hooves. Severe cases with outwardly visible clinical signs are known by the colloquial term founder, and progression of the disease will lead to perforation of the coffin bone through the sole of the hoof or being unable to stand up, requiring euthanasia. Laminae
The bones of the hoof are suspended within the axial hooves of ungulates by layers of modified skin cells, known as laminae or lamellae, which act as shock absorbers during locomotion. In horses, there are about 550–600 pairs of primary epidermal laminae, each with 150–200 secondary laminae projection from their surface. These interdigitate with equivalent structures on the surface of the coffin bone (PIII, P3, the third phalanx, pedal bone, or distal phalanx), known as dermal laminae. The secondary laminae contain basal cells which attach via hemidesmosomes to the basement membrane. The basement membrane is then attached to the coffin bone via the connective tissue of the dermis. Pathophysiology
Laminitis literally means inflammation of the laminae, and while it remains controversial whether this is the primary mechanism of disease, evidence of inflammation occurs very early in some instances of the disease. A severe inflammatory event is thought to damage the basal epithelial cells, resulting in dysfunction of the hemidesmosomes and subsequent reduction in adherence between the epithelial cells and the basement membrane.
Tendency to lie down whenever possible, and recumbency in extreme cases
Change in the outward appearance of the hoof in cases of chronic laminitis: dished (concave) dorsal hoof wall, "founder rings" (growth rings that are wider at the heel than the toe), a sole that is either flat or convex just dorsal to the apex of the frog which indicates P3 has displaced or penetrated, widening of the white line at the toe with or without bruising, "clubbing" of the foot. Change in the appearance of the coronary band: hair that does not lie in a normal position (not against the hoof wall), indentation or rim just above the hoof capsule allowing palpation behind the coronary band. In cases of sinking, it may be possible to palpate a groove between the coronary band and the skin of the pastern. Lameness evaluation
Hoof testingLaminitic horses are generally sore to pressure from hoof testers applied over the toe area. However, there is risk of a false negative if the horse naturally has a thick sole, or if the hoof capsule is about to slough. Obel grading systemThe severity of lameness is qualified using the Obel grading system:
Obel grade 1: Horse shifts weight between affected feet or continuously lifts feet up. It is sound at the walk but displays a shortened stride at the trot. Obel grade 2: Horse displays a stilted, stiff gait, although is willing to walk. It is possible to easily lift a front foot and have the horse take all of its weight on the contralateral limb.