What is Thrush?

"Thrush is an infective condition of the frog and its sulci which results in degeneration of the horn (the protective frog callous) and the production of foul smelling gray/black discharge.

In severe or neglected cases, Thrush can involve the underlying corium. Degeneration of the horn is due to infection with keratolytic bacteria and fungi, and multiple organism infections are common. Predisposing causes of thrush include wet unhygienic stable conditions, poor routine foot care, prolonged confinement, overgrown ragged frogs, and long, contracted or high heels which produce deep sulci.

Thrush doesn't always stink and have a discharge, so many owners and vets miss it. Its possible for Thrush to thrive in feet with hard dry healthy-looking frogs. Thrush contains anaerobic bacteria that flourish in tight cracks and deep central sulci.

People mistakenly believe that Thrush is something horses only get when the footing is damp and filthy, but horses in these environments can have wonderfully healthy frogs if their diet is appropriately low carb and contains balanced trace minerals.

Once established in a hoof, thrush lingers on through summers driest days, creating extreme discomfort for the horses that have it.

Thrush Prevention??

There is a dietary component to thrush, as horses on high carbohydrate diets are more likely to have Thrush, and high iron / low zinc & copper diets are common thrush triggers. If your horse has chronic thrush or poor frog development (persistently thin scrawny and dry frogs), check the diet, look at your horses weight and over-all health, balance the minerals, and if that doesn't work, try adding pro & prebiotics along with a yeast product like Yea Sac Farm Pack or Kombat Boots for a months to see if frog condition improves.

I had one client horse who was a QH that was very overweight with a large, hard neck crest. The horse was on balanced minerals and low carb hay, but the hay was free-fed and the horse had access to 1/2 acre of very stressed grass. Every spring the mare would get tender, her bars would enlarge and she'd get thin soled and pop an occasional abscess. Her frogs were very scrawny, even after 5 years of barefoot. In an almost identical case, the owner removed the access to stressed grass and controlled hay consumption using close weave hay nets, increased exercise, and two months later, the frogs responded by getting plump and wide, the thrush resolved and her neck crest had disappeared.

Diet is a huge problem for most of our horses.


Recognizing Thrush

The horse on the left has a Thrush infection that has penetrated the frog and the frog corium. He also has a bad fungal infection between the heel bulbs of his contracted heels.

Thrush, Fungus and Yeast aren't problems for all horse, because all horses have fungus or yeast activity in healthy feet - Yeast and fungus are present whenever there is a shedding frog, sole or bar - but it doesn't develop into thrush.

Fungus and yeast become a problem when blood supply, movement, hygiene, environment, diet &/or hoof care aren't what the horse requires. The resulting bacterial imbalance creates an opportunity for Thrush infections to take root.

I didn't begin looking for Thrush in every foot I picked up until I was trimming several horses whose medial/lateral imbalance wasn't responding to my trim the way similar feet had responded in the past.

These feet had extreme heel contraction, were "wry feet" (See Nipper and Samson) with the hoof capsule became distorted by the horse weighting only the outer walls . I was seeing feet with retained sole, characterized by deep commissure's, a flat sole and high bars

One of these horses, Ace, to the right, responded rapidly to soaking in the diluted Lysol solution (a soak Pete Ramey recommended for treating thrush) by having the heels relax and expand almost 1/2 inch and lower another 1/2 inch in a one week period, and I knew I was on to something.

Frog Flossing?

If your horse has tight infected heel bulbs like those above, I suggest using surgical gauze or vet wrap to carefully clean out the tight crease between the heel bulbs, using something like Vetricyn to cleanse it thoroughly. Using a cream like Zinc Oxide ointment, Dry Cow or triple antibiotic cream will help heal the infected and inflamed skin. See the Thrush Solutions page for more treatment ideas.


The unshod horse at the left has wall separation and the flat sole, high bars and deep commissure's that are symptoms of thrush. In this case the thrush is obvious. The owner had been fighting it with over-the-counter treatments for 3 years

On the right, deep commissure's and a solid, flat sole with high bars create a "cast" for the hoof to disable hoof mechanism when a horse has a painful case of thrush. This horse is sound barefoot on trails - until he hits a rock in the frog area!


This owner argued that her horse had a great frog, and at first glance it looks okay, but the horse fought violently when I gently probed the central sulcus. The first clue that he had thrush? Look at how he stands, leaning forward slightly so to not press those sore frogs against the ground!

This frog felt "spongy" when I tapped it with the hoof pick, and when I gently pried the edge up, the frog lifted up, attached by shreds of thrush-eaten frog material just below the surface.


The Before and After pictures above are of Ace , who had historically high, contracted heels. Prior farrier's tried to lower his heels unsuccessfully over an 8 year period, and I was certain that taking him barefoot would resolve the height.

After 6 months barefoot, I tried lowering the heels slightly and he was immediately tender. His frogs looked fine and his owner was extremely careful about keeping his feet pristine. But as I looked at the tightly contracted heels, my suspicions grew. She was insulted when I asked her to soak for thrush, and, asking her to humor me, I suggested that she soak his feet in a mild Lysol dilution for 20 minutes a day for 5 days the week before I was due to re trim. I took the Before shot, above, before leaving.

When I returned for the next trim, she was still feeling insulted but let me know that she had done as I asked, but soaked for 40 minutes a day for 7 days, just to be sure.

His heels had de contracted 1/2 inch, his high bar and 1/2 inch of retained sole in the heel area shed voluntarily, and we were left with the After shot on the right.

Navicular Symptoms? Severe Imbalance? High or Under Run Heels? Thick Sole?
Undiagnosed Lameness? Check For Thrush!!

The primary symptom of thrush is a painful frog resulting in an inability to load the heels normally. I made a list of the associated symptoms and came up with a long list that I've seen in thrushy horses: Thrush is not about an odor, it's about a painful sensation!

  • Resistance to having feet picked up and cleaned or inspected
  • "Wry Feet" - walking on inner or outer walls until they have been worn into the live sole,
    leaving the opposite walls longer
  • Thin, scrawny, distorted or displaced frogs
  • Growing tall bars that are active and may extend around the frog
  • Toe first landing when the foot looks healthy
  • Deep commissure's and flat soles in the rear of the foot
  • Contracted heels that won't relax and spread
  • Club feet that began mid-life, or after an injury or laminitic attack

I began to treat any horse with the above symptoms as if they had Thrush even if it wasn't evident, and all of them responded positively, even when the symptoms were chronic and extended back several years. So I started being very careful about how I trimmed frogs and eventually started examining diets looking for an underlying cause. Mineral balancing and supplements like California Trace that supplement adequate amounts of copper and zinc.

Thrush is easy to spot if you know where to look, even in a dry frog.

I have worked on more than 30 horses who were diagnosed with "navicular syndrome" or an unspecified lameness, including several horses that have been lame for years, and all were "cured" by a good barefoot trim followed by treatment for Thrush using Oxine, Usnea, Pete's Goo triple antibiotic, Dawn dish detergent, Lysol or White Lightning. See the Thrush Treatments page here for more info. In recent years I have had faster success when clients have adjusted their horses diets.



If your environment doesn't scour your horses bare feet thoroughly as he or she moves, that job is shared by the you and your hoof care provider. Remember that your hoof care provider can't see your horses feet once every 4 to 6 weeks and put a good foot on your horse in one visit! Dietary management, cleaning and maintenance has to occur on a regular basis.

The lucky or savvy among us use pea gravel to do that interim maintenance! The primary cause of the thrush I see is a damp, urine and bacteria contaminated environment. Paddocks filled with damp chipped wood are difficult to keep clean, and residual manure and urine are a bacterial reservoir that repeatedly infects frogs. Worse environments are paddocks that carpeted in deep manure mud or manure dust.

Pea gravel laid 4 to 6 inches deep provides the best environment for healthy feet. The gravel drains well and scours the feet to remove tattered frogs and lose sole.

The round gravel in the picture on the right worked great, but a smaller 1/4 inch pea gravel is easier to keep clean. See the Passive Conditioning Page   Thrush isn't always caused by a poor environment, but its a common culprit.

Hoof Hygiene

Owners should be able to use a sharp hoof pick with a point as sharp as a pencil to deeply and thoroughly probe the entire sole and frog, including the central sulcus, using between 3 to 5 pounds of pressure. If your horse won't stand for having his feet cleaned, hose the feet out thoroughly, scrub the cracks and crevices with Dawn dish detergent and a long bristled plastic scrub brush (a regular floor scrub brush works fine), rinse thoroughly and treat them for thrush.

Most horses "bad manners" for foot handling are a response to the pain of having thrushy feet cleaned. To guard against thrush, encourage your farrier to remove ONLY the shedding frog, cracked loose frog and "tags" that can hide debris in the sulcus and commissure, providing a nursery for thrush. Pick your horses feet daily if they stand in urine or if you have spotted symptoms of thrush!

If your horse won't stand for having his feet cleaned, check the bottom of his feet for a shedding frog or thrush. Most horses "bad manners" for foot handling are a response to the pain of having thrushy feet cleaned. When a horse resists lifting a foot? Thrush is a likely reason!


Trimming the Frog

If your horse has severe thrush and resists frog trimming. you may need to soak the horse repeatedly to treat the thrush and have your trimmer of farrier come out a later to work on the frogs. 

Working on painful frogs is hazardous business, the pain response is equal to working on an open wound, is so be careful!  Topically treating the frog with Usnea Tincture relieves the pain and sometimes makes trimming easier, but if the frog is filthy, it may take $20 of Usnea to cut through the filth!

Better to wash the frog thoroughly, scrub it and soak it in Oxine several times and trim the frog when the pain has subsided.

A healthy shedding frog isn't something owners should be afraid of maintaining between trims because there isn't a thrush infection, only health yeasts and fungus. By the time a frog begins to shed, it is a flap of insensitive tissue that can be trimmed as if it was a flap of dry skin. Don't pull it off unless it comes loose with minimal pressure.

You can also use pruning sheers like the Corona AG 5030 Grape Sheers above to remove frog flaps.. Corona sheers are are easy to sharpen, have a curved edge and blunt tip. They are an inexpensive tool for trimming frogs, cutting bale twine and as a general stable shear. They are found on-line or in garden centers.

Other tools for removing bits of lose frog include hoof knives, wire hardware brushes, hoof nippers, large sizzor-type nail nippers or any similar tool. hardware brushes are great for removing tattered frog and loose sole!

Below, I'm using a stainless steel bonsai "knob cutter" gardening tool, available online. These and Bonsai Concave Trimmers are great for removing frog tags as well as cleaning up chestnuts.


Frog Conformation

A healthy frog is thick and full with a tough leathery texture when it's mature, This durable protective covering is called the Horn. An immature frog still looks healthy with a leathery skin, but smaller and undeveloped.

A frog that's shedding has a loose horn and feels spongy, and it may be loose enough that it can be pulled back from the emerging immature frog, which is often covered with a white cheesy looking layer of yeast and occasionally a little black thrushy film around the edge. Leave any old frog that is securely attached, snipping of shedding portions. You can use a hoof knife to **very gently** scrape off yeast and dark thrushy film, but if left alone it will wear off quickly.

Unhealthy frogs run the gamut from shriveled frogs entombed between contracted heels, to chronically shrunken frogs, to "greasy" looking thrush filled frogs. For pictures of health frogs look at the healthy frog pages heres;Healthy Fall Frogs, More Healthy Frogs


If the horses diet, movement and environment are good and there is no pathology in the hoof, yeast and fungus usually don't create problems; they are part of the hoof's symbiotic environment. This is why I'm opposed to things like disinfectant foot baths and constantly treating for thrush even though the frog is healthy and hard. Its like over dosing your horse on unnecessary supplements, antibiotics and wormers.

Too much of a good thing is a bad thing.

YEAST is the white stuff that coats the new frog when a frog has shed. Yeast in a healthy foot IS okay and doesn't need to be treated. Treating it is over-kill..

FUNGUS is the black stuff you see when you pick out your horses feet for the first time in a few days.

THRUSH is a combination of yeast, fungus and anaerobic bacteria, and it always needs to be treated AND prevented by balancing the diet. .