A bone, or jack, spavin is a bony enlargement on the lower interior surface of the hock joint that may result in limited flexing of the hock. Spavin lameness typically results in an irregularity of gait. Faulty hock conformation, excessive concussion, nutritional deficiencies, and hereditary predisposition are considered causes of a bone spavin, but a traumatic event, such as jumping or vigorous training, is usually required to cause its development.
Resources
Evans, Borton, Hintz and Van Vleck. The Horse. 2nd edition. W.H. Freeman and Company, 660 Market St., San Francisco, CA 94104, (415) 391-5870.