Angular limb deformity (ALD) refers to a lateral (outward) or medial (inward) deviation of a limb. The angle point of most limb deformities is associated with a joint. The carpus (knee joint) is, by far, the most common joint affected. The fetlock (ankle joint) and tarsus (hock joint) can also be affected. Angular limb deformities occur in foals of all breeds. There does not seem to be any higher incidence of the problem in colts compared with fillies. Foals can either be born with deviated limbs (congenital) or develop the problem later (acquired) during their first year of life when rapid changes are occurring in the bone and joints.

Equine sarcoid is the most commonly diagnosed tumor in horses and accounts for up to 33% of all reported equine tumors. Sarcoids may arise either spontaneously, or at a site of previous skin trauma. They develop from a specific cell in the skin called the fibroblast. The mechanism of this uncontrolled growth of fibroblasts in unknown, but a virus (papillomavirus) has been implicated. There is no sex or breed predilection, however, age may play a role as the majority of sarcoids (~ 70%) occur in horses less than 4 years old. The most common sites of the occurrence are the head, ears, limbs, and ventral abdomen.

The disease typically begins with extremely heavy sweating all over, followed by the development of patchy sweating under the mane and between the legs over a period of 1-3 months. As the ability to sweat is progressively lost, the horse will begin puffing and blowing forcibly after exercise in efforts to compensate heat loss. A dry coat, thinning hair on the head and upper neck, and poor stamina are also symptoms of the disease. In more severe cases, the horse may develop “heat overload” and collapse during strenuous exercise.

Angular Leg Deformities in Foals. Angular limb deformities in the foal are defined as a deviation from normal alignment when viewed from the front. The deviation from normal may be in any of the joints or long bones of the legs. The deviation is seen as a lateral (outward or valgus) or medial (inward or varus) bowing of the limb usually at a joint. Deformity may involve the front and rear legs.