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Do you Know the Lowdown on Thrush?

By Cynthia McFarland

Once you've smelled it, you know it. There's no mistaking the distinctive foul odor of thrush in a horse's hoof.

Thrush is caused by opportunistic microbes that are found in animal feces and many soils. In other words, where most horses live on a daily basis. These microbes flourish in dark, moist places, making a dirty equine hoof the perfect host, in particular the grooves (sulci) on either side of the frog.

Setting the Stage
The horse's foot naturally has crevices and folds that can easily trap debris and organic material--a polite word for manure. If hooves stay damp and aren't trimmed and cleaned out regularly, they can offer an ideal environment for thrush to develop. 
Once thrush sets in, there is typically an offensive-smelling black material on and in the frog of the foot, as well as the sulci. Left untreated, thrush can affect the sensitive layers of the hoof, and possibly even result in lameness.

Before you beat yourself up if your horse has thrush, realize that some horses are more susceptible that others. For example, horses with contracted heels or some form of lameness--especially in the heel area--tend to get thrush more easily.
Old horses that aren't active and horses that aren't exercised regularly--including those who spend a lot of time in a stall--can also be more prone to thrush.

Horses with normal, healthy hooves will "self clean." You've likely found those packed clods of dirt/manure, usually complete with perfect frog imprint, out in the pasture. 
They naturally come out of the hoof as the horse is moving. If the horse isn't able to get out and move around freely, has overgrown feet, or some hoof conformation defect or lameness, his feet won't easily clean themselves, meaning thrush is more likely.

Effective Management

Before you head for the tack store to pick up a bottle of thrush treatment, call your farrier. In order to manage the problem, you must be able to get that product where it needs to go.

"If the frog has succumbed to thrush, you need to debride the loose flaps and cut away the necrotic areas. If you don't do this, the topical treatment can't penetrate the area to kill the remaining microbes. When your farrier trims the area, the bulk of the microbes will be removed, but you still need that topical treatment to finish it," explains Travis Burns, a Certified Journeyman Farrier, who is a Lecturer and Chief of Farrier Services at the Virginia-Maryland Regional College of Veterinary Medicine. 

"The first step is debriding the frog to a healthy-appearing margin and then using a product made to treat thrush," says Burns, noting that there are a number of commercial products on the market from reliable manufacturers that work well. (Don't rely on home remedies or Internet advice such as using bleach or formaldehyde to treat thrush!)

Read directions carefully and don't allow thrush products to come in contact with skin or hair--yours or the horse's. It's always a good idea to talk to your veterinarian if your horse has a thrush infection, just to be sure you are using the right product(s) and treating it properly. 

Be sure to treat the affected area long enough to completely clear up the problem.

before you head for the tack store to pick up a bottle of thrush treatment, call your farrier.

Avoiding Thrush

"It has been proven that most of the microbes that cause thrush are anaerobic, meaning they live only in environments without oxygen," says Burns, explaining that this is why picking out the feet regularly to expose the bottom of the foot to UV light and air is indicated. Doing so exposes the area to oxygen and kills those microbes.

In most cases, thrush is basically a management concern and can be prevented by conscientious horse-keeping. 


Even in horses that are predisposed to thrush, such as those with clubby feet or contracted heels, you can limit thrush.

  • Pick feet out daily
  • Inspect carefully for any problems developing
  • Provide clean, dry bedding 
  • Keep hooves trimmed regularly by a competent hoof care provider

If you go too long between farrier visits, your horse's frog will have more flaps, folds and pockets that can trap debris and microbes. The foot will also be less balanced, which may negatively impact movement. This is another reason for scheduling a regular visit, as well as cleaning out the feet each day.

"If you see or smell signs of thrush, early treatment is always better than trying to deal with it down the road," says Burns. "Thrush isn't a complicated thing, but it does put an owner to work to eliminate it."

Thrush Tip #1: Regular Hoof Care Helps Prevent Thrush

Improper trimming, going too long between farrier visits, and not regularly cleaning out the feet will contribute to thrush, which is caused by anaerobic bacteria and dark, moist conditions. Pick out those hooves every day and keep your horse on a regular schedule with your hoof care provider. This is important even for horses that aren't ridden--including that old retired gelding in the pasture and the pony you got as a companion animal.

Thrush Tip #2: Exercise Important in Avoiding Thrush

Horses are made to move. Regular exercise can also help prevent and treat thrush, even for horses that live in pristine environments. Regular exercise promotes blood flow, which is essential for healthy feet. Another reason to get your horse out of that stall as much as possible.

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