Smelly feet are more than an embarrassment for horses. A noxious rotting odor emanating from the underside of a hoof is a distinct sign of a fungal infection called thrush. The responsible organism, Spherophorus neaophorus, eats away at the tissues of the frog, leaving a blackish ooze on the surface. Thrush rarely causes lameness and poses no major health hazard. But if you encounter the condition in your barn, you will want to review--and probably revise--your management routine.

Thrush thrives where horses are confined in filthy conditions. A horse who is exposed to "clean" mud that is more or less free of manure and urine isn't especially likely to develop thrush, but one who stands in urine-soaked bedding for most of the day is a prime candidate. Horses with overgrown or contracted hooves, those who wear hoof pads, and those who get very little exercise are also more susceptible to the condition. Likewise, a horse who is chronically lame as a result of another problem often develops thrush in the hoof of the affected leg.

Getting rid of thrush requires an attack on two fronts. First, you need to kill the invading fungus and-despite what directions on commercial products may say-pouring a thrush remedy over the frog will not get the job done. S. necrophorus lives in the many cracks and crevices of the hoof, and a simple splash of liquid will roll right over these hiding spaces. Packing a hoof with any product is potentially dangerous because excessive pressure can kill sensitive frog tissue. 

Here are four easy steps to treat thrush by delivering medication into the areas where it is most needed without damaging surrounding tissues. This technique, which is most effective if applied daily, is suitable whether you use a commercial or homemade preparation.

1. Make your own cotton swab by wrapping a wisp of loose cotton tightly around the end of a hoof pick

2. Soak the cotton in treatment solution. We are using a commercial preparation, but bleach also works.

3. Swab down the sides of the frog as if you were picking out the hoof. The goal is to get into all the cracks, so don't be afraid to apply a bit of pressure. (This hoof was recently shod. If there are flaps or shelves of compromised frog, have your farrier pare them away so the fungus is easier to reach.)

4. Swab the cleft of the frog and any other crevices in its surface. The swab will become darker as you work, a sign it is picking up exudates and dead tissue. Repeat the process, using fresh cotton, until the swab comes out of the hoof nearly as clean as it went in.

An ounce of prevention: Some horses are prone to thrush and have recurrent episodes no matter how clean their environment is kept. For these horses, a daily preventive swabbing can control the problem. Using straight bleach or a commercial thrush product every day can dry out the frog, however. Instead, make a gentler preparation of half bleach and half glycerin or glycerin-based hand lotion. Apply this solution to the hoof a few times a week using the hoof-pick swab technique.

The second--and most important--aspect of treating thrush: changes in the affected horse's living arrangements. Resolve to keep cleaner, drier stalls and increase your horse's exercise time. Better yet, try continuous turnout in a clean field. Not only will these changes help clear up a case of thrush, but it will prevent its return.