Autumn is just around the corner and, for many areas of the country, that means the onset of wet weather, a reduction in riding, and more stall time for horses. For some owners, it’s less time spent with their horses and more time spent snugged up on the couch with the remote. All of which could mean an uptick in the risk of your horse developing thrush–that gunky, smelly, black discharge oozing from the bottom of his hoof.

Thrush is an anaerobic bacterial infection that slowly eats away at the horse’s hoof tissue. “It’s characterized by black, malodorous necrotic (dead) material or exudate in the central or collateral sulci of the frog (the grooves adjacent to and in the middle of the triangle-shaped frog),” says Steve Adair, DVM, MS, Dipl. ACVS, associate professor of equine surgery at the University of Tennessee.

Early stages of thrush only involve superficial tissues and don’t cause lameness. But if ignored, the infection can advance into sensitive tissues and internal structures of the foot, such as the digital cushion, hoof wall, and heel bulb, warns Ashley G. Boyle, DVM, Dipl. ACVIM, assistant professor of medicine in the section of field service at the University of Pennsylvania’s New Bolton Center.

Causes

The primary factors favoring thrush are excessive hoof contact with moisture and a lack of regular foot care, either of which can occur when autumn rains and cold weather cause an owner to be less diligent about mucking the stall, picking out hooves, or turning out/exercising the horse (movement across dry ground produces a scouring action on hooves)