spavin (spăv`ĭn), disease of horses affecting the hock joint. There are two types—bog spavin, in which the hock joint is distended as a result of the collection of synovial fluid; and bone spavin, the bony enlargement of the bones that constitute the hock joint. The latter is a form of arthritis and causes inflammation, swelling, and lameness. Spavin can be caused by faulty conformation, strain, or excessive concussion. Treatment consists of rest, corrective shoeing, the application of blistering ointment, and surgery.