What is "bog spavin"

Spavin \Spav"in\, n. [OE. spaveyne, OF. esparvain, F. ['e]parvin; akin to OF. espervier a sparrow hawk, F. ['e]pervier, fr. OHG. sparw[=a]ri (G. sperber), fr. OHG. sparo sparrow, because this disease makes the horse raise the infirm leg in the manner of a sparrow hawk or sparrow. See Sparrow.] (Far.) 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.

bog \bog\ (b[o^]g), n. [Ir. & Gael. bog soft, tender, moist: cf. Ir. bogach bog, moor, marsh, Gael. bogan quagmire.]

1. A quagmire filled with decayed moss and other vegetable matter; wet spongy ground where a heavy body is apt to sink; a marsh; a morass.

   Appalled with thoughts of bog, or caverned pit, Of treacherous earth, subsiding where they tread.
   --R. Jago.

2. A little elevated spot or clump of earth, roots, and grass, in a marsh or swamp. [Local, U. S.] Bog bean. See Buck bean. Bog bumper (bump, to make a loud noise), Bog blitter, Bog bluiter, Bog jumper, the bittern. [Prov.] Bog butter, a hydrocarbon of butterlike consistence found in the peat bogs of Ireland. Bog earth (Min.), a soil composed for the most part of silex and partially decomposed vegetable fiber. --P. Cyc. Bog moss. (Bot.) Same as Sphagnum. Bog myrtle (Bot.), the sweet gale. Bog ore. (Min.)

   1. An ore of iron found in boggy or swampy land; a variety of brown iron ore, or limonite.

   2. Bog manganese, the hydrated peroxide of manganese.

      Bog rush (Bot.), any rush growing in bogs; saw grass.

      Bog spavin. See under Spavin.

n. spavin caused by collection of fluids

Bog spavin is a swelling of the tibiotarsal joint of the horse's hock which, in itself, does not cause lameness. The joint becomes distended by excess synovial fluid and/or thickened synovial tissue bringing about a soft, fluctuant swelling on the front of the joint, as well as in the medial and lateral plantar pouches. Bog spavin is generally an indication of underlying pathology within the joint.