grease heel

noun

ˈgrēs-, ˈgrēz- 

: a chronic inflammation of the skin of the fetlocks and pasterns of horses marked by an excess of oily secretion, ulcerations, and in severe cases general swelling of the legs, nodular excrescences, and a foul-smelling discharge and usually affecting horses with thick coarse legs kept or worked under unsanitary conditions

called also greasy heel

see grapes sense 1