Horse Illustrated Magazine

If you have horses, chances are you’ll see thrush firsthand sooner or later. Thrush is a bacterial infection, though it’s thought that yeast and fungal infections might also contribute to it.

With its black, tar-like, oderiferous discharge, it’s easy to spot—and smell—as you clean the sulci (grooves) along the sides of the frog. The sulci may also look deeper than normal if thrush has set in. If the infection has penetrated sensitive tissues, the horse will flinch when the area is cleaned or pressed with a hoof pick. In severe cases, the horse can be lame.

If caught early, thrush is usually quite easy to treat and resolve. If left for a period of time, thrush will not only eat away the frog, but it can penetrate the sole and work its way into vital structures. Another incentive for finding and treating thrush early is that once the infection enters the lower areas of the frog, it can be difficult to cure because most topical treatments can’t reach all the deep nooks and crannies.

While thrush is most often seen in horses that must stand in muck and wet conditions, it’s also found in horses with dry stabling. It can occur toward the end of a shoeing cycle, when flaps of the frog grow over the sulci and trap dirt and moisture. Horses with contracted heels can be prone to thrush because their hoof conformation narrows the sulci so dirt and manure aren’t as easily dislodged.

Prevention:

• Daily hoof picking is a key to preventing thrush. Be sure to really clean out the sulci rather than just picking out the sole.
  
• Regular exercise contributes to overall hoof quality by increasing circulation.
  
• A clean, dry environment helps prevent the organisms that cause thrush.

Treatment:

• Trim the frog. Have your farrier evaluate your horse’s hooves if you suspect thrush. If the frog is overgrown, the farrier will trim it. This gets rid of the infected parts of the frog and allows air to circulate better around the frog. If the frog isn’t trimmed first, all the anti-thrush products in the world won’t help.
  
• Clean the hoof. After the frog is trimmed, scrub the entire foot with a stiff brush and warm water. Allow the foot to dry completely before applying a thrush product.
  
• Apply topical product. Any tack store or catalog will offer a variety of thrush products. From thick ointments to liquids, all promise to treat thrush and kill the infection. Ask your vet for his or her advice on what works best in your area and given your particular conditions.

Other Remedies:

• Strong (7%) iodine. This can be effective for mild cases of thrush that don’t penetrate into the deep layers of the frog. However, it can also dry the hoof if used too often.
  
• Bleach. You might hear that household bleach is a good product for treating thrush, but it’s not recommended. Besides overdrying the hoof and frog, it doesn’t really kill the infection. Plus, bleach can cause significant damage to sensitive internal structures of the hoof if the thrush has created deep pockets of infection that lie next to the structures.
  
• Continue ongoing care. Pick out the hooves every day and keep the horse in a clean, dry environment until the problem clears up. The horse doesn’t have to be kept in a bedded stall, but be sure he has dry places to stand for most of the day. Rubber mats can be a lifesaver for those who must contend with mud in winter and spring. Once the thrush is cured, strive to maintain this dry, clean environment.

If your horse is troubled with frequent bouts of thrush, consult your vet and farrier.

Further Reading
Guide to Horse Hoof Problems
Eight Hoof Care Myths

The author has handled horse hooves for 20 years and has suffered only one broken toe.