Learn about this common condition from farriers and horse owners who have managed it

Thrush, an infection of the horse’s hoof tissue known for the black, necrotic (dead), stinky material it causes, is one of the most common hoof issues horse owners encounter. According to the 2020 American Farriers Journal Farrier Business Practices survey, more than half of farriers see a case of thrush each week during the year. Another 20% see thrush monthly, while 8% only deal with it a few times a year. For some farriers, thrush is only a seasonal concern when rains create persistent muddy conditions.

“Thrush thrives in dark, damp, warm environments,” explains Mike Isles, CF, APF-I, owner of MFI Farrier Service, near Saratoga, New York. “The bottom of the horse’s hoof is a petri dish for thrush.”

The hoof’s underside doesn’t get much light because it’s in constant contact with the ground, which is a natural host for millions of microorganisms. When mud, muck, and manure pack into the hoof and remain there, anaerobic bacteria can flourish, infecting the frog tissue and eating away at it.

Unsanitary living conditions and excessive hoof dampness are primarily to blame for thrush, so keeping the hooves clean and giving the hoof time to dry is essential.

“The biggest thing with thrush is to clean out the horse’s feet,” says Isles. “Ideally, once a day, but at least whenever you see your horse, especially if you’re using a topical treatment for thrush. Medication needs to get on the tissue, and if the hoof isn’t clean, the dirt is just soaking up the treatment.”

Thrush might sound like a straightforward condition that can be remedied with good horsekeeping skills. But mud, dirt, and manure are not the only culprits.

“Thrush is a bit of an enigma,” says Steve Kraus, CJF, head of farrier services at the Cornell University College of Veterinary Medicine, in Ithaca, New York. “It’s interesting because some horses can live in terrible conditions and never develop it, while horses in good conditions can. So, thrush is not necessarily caused by bad health care or bad conditions but aggravated by it.”

Horses that have compromised immune systems are susceptible to thrush, says Kraus. Horses with genetically weak hooves or horses that have an inability to absorb key trace minerals such as zinc, which is needed for healthy hoof tissues, might also be more likely to develop thrush, he added