Degenerative Joint Disease, commonly known as bone spavin, is a bony swelling on the lower, inner side of the hock, caused by arthritis of the bones in the area. Some horses with an obvious bone spavin show little or no signs of lameness; others may be very lame but with no signs of swelling. Horses with bone spavin may still be useful, but fluctuating lameness may recur at varying intervals.
When a horse is viewed from behind, a line should bisect the gaskin, hock, cannon, fetlock, pastern and foot. If the horse's hocks turn inward, the horse is considered cow-hocked. When the legs are viewed from the side, a straight line drawn downward from the back of the buttock should touch the back of the hock, cannon and fetlock. If the horse has too much angle in the hocks, then it is considered to be sickle-hocked. If the leg is forward of this line and too straight, the horse is considered post-legged.
In many cases, bone spavin is due to poor conformation, such as sickle and cow hocks. Despite what many people think, the condition is not hereditary. What is inherited is the poor conformation. Bone spavins, bogs, thoroughpins and weakness are common among sickle-hocked horses. The condition can also be caused by stress and strain being placed on the hock because of participation in such activities as polo, calf roping and racing, especially by young horses.
Signs include a hard, bony enlargement that can be felt and seen in the lower and inner side of the hock. Lameness is evident when the horse is cold but often disappears as it warms up with exercise, although in some cases the lameness may worsen. The lameness is characterized by reduced flexion of the hock and a shortening of the stride in the affected leg.
Accurate diagnosis is important to determine the severity of the condition, and this in turn will determine the type of treatment. The diagnosis can only be made by your veterinary surgeon with the aid of X-rays. Your veterinarian may advise any one of a number of treatments or a combination of them, if necessary. These treatments include rest in a spelling paddock for a minimum of six weeks and corrective trimming and shoeing. In the latter treatment, the toe of the foot should be rasped square and a shoe with a raised heel and a rolled square toe should be fitted. This causes the leg to move in a straight line rather than deviating outwards, thus alleviating strain on the inside of the hock.
Other treatments are radiation, anti-inflammatory drugs, pin firing and surgery to sever a section of the tendon that runs over the spavin.