Thrush in horses is an unpleasant infection of the central and collateral grooves of the frog.
Keratonolytic (keratin-dissolving) bacteria, including the sheep foot rot organism Fusobacterium necrophorum, attack the softened tissues of the frog, causing it to rot away.
Signs of thrush
The most obvious sign of thrush is a foul-smelling, black discharge from the frog, which itself may have softer spots and appear irregular in shape. Despite the offensive smell and discharge, many horses with thrush show no obvious discomfort or lameness.