What does "spavin" mean?

Spavin: A disease of horses characterized by a bony swelling developed on the hock as the result of inflammation of the bones; also, the swelling itself. The resulting lameness is due to the inflammation, and not the bony tumor as popularly supposed. Harbaugh. Bog spavin, a soft swelling produced by distention of the capsular ligament of the hock; -- called also blood spavin. -- Bone spavin, spavin attended with exostosis; ordinary spavin.