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Thrush Treatments Summary
Treating Thrush with White Lightning
Hoof Soaking Techniques
Hoof Soaking Solutions

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.

There may be a dietary component as well, as horses on high carbohydrate diets seem more likely to have Thrush. Unfortunately, Thrush doesn't always stink and have a discharge, and many owners and vets miss it. Its possible for Thrush to thrive in feet with hard dry frogs. Thrush contains anaerobic bacteria that flourish in tight cracks and deep central sulci.

People mistakenly believe that Thrush is something horses only have when the footing is damp and filthy. Once established in a hoof, thrush lingers on through summers driest days, creating extreme discomfort for the horses that have it.


This horse 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 horses. Most horses have some fungus or yeast activity in healthy feet - it's present whenever there is a shedding frog, sole or bar - but it doesn't develop into thrush.



Deep commisure'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!


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

I didn't begin looking for Thrush in every foot I picked up until mid July a few years ago.

At that time, I was trimming several horses whose hoof capsule imbalance wasn't responding to my trim the way imbalanced feet had responded in the past.

These were feet with extreme heel contraction, "wry feet" (See Nipper and Samson) where the hoof capsule became distorted by the horse weighting only the outer walls and feet with excessively tall heels. I was also seeing feet with what appeared to be a retained sole, characterized by deep commisure's with a flat sole and high bars (example above).

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.



The unshod horse above has wall separation and the flat sole, high bars and deep commisure'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.

The recently unshod foot shows a characteristically thrushy frog as well as thrush invading the separated white line.

Symptoms of a painful hind foot are:
- the stretched long toe. The frog should be approximately 2/3 of the length of the foot; a longer toe is a symptom of chronic toe-first landings
- weak digital cushion and contracted heels
- high bars


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 actually 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 ( see his case study) , who had historically high, contracted heels on both front feet.

Prior farrier's had 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 asked her to 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 decontracted 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:
  • 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 commisure'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
  • Seasonal unsoundness

I began to treat any horse with any of the above symptoms for Thrush even if it wasn't evident, and all of them responded positively, even when the symptoms were chronic and extended back several years. Their owners are shocked because many of these horses feet don't stink, and the thrush isn't readily visible. In a few cases, it was deep in the frog, at the corium level.

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

I now (Fall, 2008) have more than 30 horses that have been seen by qualified vets and at vet facilities who were diagnosed with "navicular syndrome" or an unspecified lameness, including several horses that have been lame for years, who 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 many cases, thrush is misdiagnosed as Navicular.


No matter who's caring for the feet, when we focus on the wall, we usually ignore the frogs. Thrush is a frog disease.

For most of us, our horses have had thrush to varying degrees for years. Some of us haven't recognized it, and when we did, we were usually unable to completely cure the infection.

Impaired blood circulation ranks high on the list of causes of thrush. Why? Thrush is a symptom of other underlying problems. The three most significant underlying problems are 1) impaired circulation due to "peripheral loading" 2) incorrect landing (toe first vs heel first) and 3) dietary imbalance & / or a too-rich diet.

According to Dr Bob Bowker and Dr Diane Isabel, the circulation in a shod or peripherally loaded hoof is approx. 20% of what it is in a healthy barefoot hoof. On top of that, most shod horses land toe-first or flat. The primary problem in these feet isn't thrush, its impaired circulation and incorrect use of the foot. Its important that people understand this when trying to clear thrush up in a shod hoof, and taking shoes off for the winter might help shod horses get past the thrush. I find Thrush in approx. 90% of the horses I take shoes off of, and once its completely cleared, it rarely comes back.

But thush isn't just about shoes. Thrush is a problem when there are dietary, hygene, metabolic, imbalance and patholgy problems.

Thrushes common denominators are:

  • Poor Past Trimming or Shoeing  - Almost every horse that I take out of shoes has some thrush and other signs of a chronic toe-first landing. Barefoot trimmers need to know that they can contribute to thrush, too! Toes that include a lamellar wedge (long toes) prohibit correct movement, and untrimmed frogs and undiagnosed thrush are a component of good hoof maintenance.
  • Past Injuries - Horses with injuries that result in favoring a foot often end up with a contracted heel on that foot, and any contraction results in cracks that welcome Thrush's anaerobic bacteria.
  • Hoof Hygiene - Does the horse stand in damp footing that contains Urine? Urine contains Ammonia, and Ammonia dissolves the proteins in the frog! Are the feet picked out regularly? Are the frogs trimmed in an appropriate manner? Is footing dry and clean or soupy filth?
  • Frog Conformation - Open and calloused, atrophied or over trimmed? Frogs with deep cracks, crevices and flaps are most susceptible to Thrush, as are frogs robbed of their protective Horn.
  • Hoof Capsule Conformation - Are heels contracted or open? High heels or low? Is the outer wall worn too short, or is the inner wall too long? Horses will walk on the sides of their feet or favor their toes when they have thrush to avoid "hoof mechanism", the flexion in the hoof that enables shock absorption. Good blood circulation is necessary for a healthy frog, so good heel-first movement is a priority.
  • Environmental Deficiencies - What is footing like? Is it clean and dry or damp? Does the organic material provide a refuge for bacteria and ammonia?
  • Diet - Does the horse have a rich diet that emphasizes grains rich forage and alfalfa, or is it a grass based low carb diet?
  • Exercise - Horses need to move; is there adequate room for the horse to move and stretch, or is he given adequate exercise opportunities?

If a horse endured a poor hoof care or hoof hygiene in the past, it's likely that impacts the foot the horse uses today.



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.

I suggest that people scrub feet out when bathing their horse or on a weekly or monthly basis to prevent Thrush from starting. 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 commisure, 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 trimming. you may need to soak the horse repeatedly to partially treat the thrush and have your trimmer of farrier come out a later to work on the frogs. 

Working on these extremely painful frogs is hazardous business, the pain response is often stronger than if you are working on an open wound, is so be careful!  Topically treating the frog with Usnea Tincture relieves the pain and sometimes makes it 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, then trim when the pain has subsided. That said, a healthy shedding frog isn't something owners should be afraid of maintaining between trims.

By the time a frog begins to shed, it is a simple flap of insensitive tissue that can be trimmed as if it was a flap of dry skin. Don't pull it off! Use pruning sheers like the Corona AG 5030 Grape Sheers above to remove the part that's lose. These sheers are wonderful because they are easy to sharpen, have a curved edge and blunt tip. They are also inexpensive tool for trimming frogs, cutting bale twine and as a general stable shear. They are easily found on-line or in garden centers.

Other tools for removing bits of lose frog include hoof knives, exacto knives (be VERY careful!), wire hardware brushes, hoof nippers, large sizzor-type nail nippers or any similar tool.

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


Frog Conformation

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

A frog that's shedding has a loose Horn and feels spongy as opposed to hard. 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 frog that is securely attached, snipping of lifted portions, and use a hoof knife to **very gently** scrape off yeast and dark thrushy film.

Unhealthy frogs run the gamut from shriveled frogs entombed between contracted heels, to chronically shrunken frogs, to "greasy" looking thrush filled 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 and may be healthy. They are a 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 supplements, antibiotics and wormers.

Too much of a good thing is always 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. FUNGUS can create problems if left in the foot for extended periods of time if the hoof is compromised at all.

THRUSH is a combination of yeast, fungus and anaerobic bacteria, and it always needs to be treated. If I'm not sure if the yeast and fungus are in balance? I choose something mild like a little Usnea tincture or Dawn scrubbing. Save the big guns like Oxine for when you really need it.


See the list of related pages at the top of this page!

The best "cure" for Thrush is soundness, a good diet, a dry environment, a good trim, regular frog-checks and scrubbing if needed, exercise and if at all possible, a patch of deep, dry Pea Gravel in the horses favorite loafing area.
Linda Cowles Hoof Care
Serving the greater SF Bay Area & Northern California
Copyright 2008 Linda Cowles
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