Thrush: Much More than a Cosmetic Flaw                         

Horseback Magazine                                                     12-10-13                                                                  Pete Ramey

Thrush is a common catch-all phrase for the wide assortment of bacterial and fungal infections of the horse's frog. It is most-commonly recognized by an extra-foul smell when picking out the hooves, by a disintegration of the frog tissue, and sometimes by a grey or black residue in and around the frog that has a texture resembling wet or dry, gray or white cottage cheese.

While most horse owners were taught to look out for thrush, most tend to think of it only as a hygiene problem or merely a cosmetic flaw. Instead, it is a serious and quite common cause of lameness, often misdiagnosed as navicular syndrome, plus it can cause a cascade of problems within the foot, and throughout the horse's entire body. 

How critical is a healthy frog?

When a horse is moving correctly, the foot should impact the ground slightly heel-first. So, on rocky terrain (or any other terrain the foot can sink into) the frog is bearing much of the initial impact force. The frog, along with the overall flexible structure of the back-half of the foot, is designed to dissipate much of the initial impact energy, as do the tires on your truck. This is healthy and natural - the way the horse was built. If there is any sensitivity in the back of the foot, the horse will avoid moving in this natural way; instead, it will shift more impact force to the front of the foot. While toe-first impacts are perfectly natural if a horse is travelling uphill, accelerating, or negotiating slippery terrain, the system was not designed to operate this way all the time - this compensative movement robs the horse of its natural front-line energy dissipation system, increasing the force that must be absorbed by joints, ligaments, tendons, muscles, etc.  This can lead to injury and/or speed up long-term breakdown. Additionally, excessive toe-first impacts can cause wall flares, hoof capsule rotation, wall cracks, thin soles, bruises, P3 remodeling, solar corium damage and abscessing.

In short, healthy frogs are important! If you have ever picked out a horse's foot and found yourself needing to be careful not to cause pain with the hoof pick, think of how difficult it would be for the horse to use the back of that foot. If the frog is healthy, it should be almost impossible to cause pain to the bottom of a horse's foot with a typical hoof pick, and the central cleft should not be deep or particularly sensitive.


The highly sensitive, deep central sulci common with desert thrush cases.

Perhaps less common than in wet environments, but causes considerably more pain.

Wet vs. Dry Conditions

Most people tend to think of thrush as a wet-environment issue. While it may be more common in wet conditions, it seems to cause more pain when it occurs in the desert. A hard, dry frog with a deeply-infected central sulcus is far more painful than a soft, wet frog with the same infection, so no matter where you live, you need to be on a constant lookout for this problem. That said, one of the best things you can do to treat and prevent thrush is to keep the horse's environment clean. It is also important to drain wet areas - you can't control how often it rains, but you can control how long the horse's footing stays wet after it rains. Adding gutters and drainage to the barn, adding gravel to low, wet, high-traffic areas, cleanup of manure and urine, and general drying out of the horse's area reaps major benefits.


 When trimming the frog for hygiene, remove thin "flaps" along the collateral and central sulci (grooves) that trap debris and block air flow into the crevices. Equally important, are the ground-surface areas you should often avoid trimming. When possible, leave these areas alone to continue callusing. It is actually quicker and easier to trim the entire frog into a neat, tidy appearance, but in many cases this can cause lameness. It is better to trim what you must, and leave what you can - prioritizing soundness over beauty. Photos reprinted from the book Care and Rehabilitation of the Equine Foot.



Left photo, this horse was very lame, gingerly walking with a pronounced toe-first impact - the only real problem I found was the thrush in the central sulcus. The heels had contracted until an exaggerated crevice allowed infection to take over. Then the runaway infection ate its way all the way up into the hairline. The same foot (right photo) is shown after 4 weeks of riding in padded hoof boots and treating as described here. The heels opened up and the lameness disappeared as the frog became more healthy. Note that there is still an area at the central sulcus that is too narrow and deep to see to the bottom of. Treatment needs to continue until the entire frog is visible. Photos reprinted from the book Care and Rehabilitation of the Equine Foot.



When trimming the frog, try to remove tiny flaps of skin that can harbor fungus and bacteria, but avoid over-trimming the frog and causing sensitivity. This tightrope walk is impossible to teach in a magazine article, but at least be aware that it is common for horses to develop painful thrush simply because of a lack of hygienic frog trimming - but it is equally common for horses to be lame or impact toe-first because of excessive frog trimming.


As with every other problem a horse might have, there is a critical nutritional component. I'll be brief, because I seem to discuss it in every article, but don't underestimate its importance. When any component is missing from the diet, the horse tends to provide what it can to the critical organs. The skin gets the leftovers. So any gap in the nutrition profile can weaken the frogs (and every other part of the horse's foot, along with the skin and coat). High-quality, well-balanced nutritional supplements are typically the best treatment (and prevention) of advanced thrush cases (I prefer California Trace Plus).

Additionally, excess sugars in the diet can weaken the frog tissue, as can any disease and even emotional stress. You have to consider the whole animal, and every aspect of its health and well-being. This will sound fruity to some, but truer words were never spoken.

Topical Treatment Solutions

Most people are surprised that I always mention the medicine last. Topical treatment is important, but not as important as the factors I previously covered (environment, trimming and nutrition). Many commercial treatments and old home remedies will work, but many of them can actually make the situation worse. Whatever you use, be sure it kills both fungi and bacteria - this is the easy part. The harder part is that the product must not harm or destroy live tissue. In advanced thrush cases, particularly at the central sulcus (cleft), the tissue at the bottom of the crevice is thin, raw, and very sensitive. Treating this area with a destructive or caustic product often causes more harm than good. I half-jokingly tell clients to find the most sensitive spot on their own body and apply any would-be thrush treatment to the area. This would quickly tell them if the remedy is appropriate to use in a sensitive area of their horse.

How to Treat

Whatever medicine you choose, it is important to treat all the way to the deepest point of the central and collateral sulci, and any other deep pockets or splits in the frog. I have only found two ways to do this effectively. First, and probably most effective, are long soaks (at least 20 minutes) in a liquid solution. This is best-done with commercial soaking boots, but homemade models can be fashioned with inner tubes or thick plastic bags. Don't try it with a bucket. It is doubtful you will be able to soak long enough or often enough to do any good. Be sure the soaking solution kills fungus and bacteria and more importantly, be sure it does not damage or excessively dry out the young, tender live tissue attemoting to grow in to fill the lesions. My preferred soaking solutions are, 1) 50/50 apple cider vinegar/water (30-45 minutes), or 2) activated Oxine AH  (4 ounces of Oxine AH, activated with either 4 ounces of white vinegar or one teaspoon of citric acid, diluted with one gallon of water, 20 minute soak in a sealed plastic bag - detailed directions here). I also like Clean Trax and White Lightning, though their price often prevents people from soaking often enough.

The other method I use is to inject a creamy or salve-type solution deep into any crevices with a catheter-tipped syringe (Monoject 412) or similar long-tipped tube or applicator. This requires great care not to damage the soft tissue, but is much quicker than soaking. See for details.

When to Treat

Generally speaking, contact with air keeps these harmful pathogens in check as well as anything. So if you can readily see the bottom of any crevices in the frog, routine hoof picking may be all you need to treat and prevent thrush problems. If, however, you pick out the foot and find deep areas (usually at the central sulcus. sometimes at the collateral sulci beside the frog) that you cannot see to the bottom of, this is a place where you need to treat. Keep treating until the area fills in and/or opens up so you can see the entire surface.

Use those same criteria for prevention - always treat any deep pockets as soon as they try to form in the future, and then discontinue treatment as soon as you can see the entire frog. Treated in this proactive fashion, it is very rare for thrush problems to develop to a point that they cause pain for the horse, and as usual, it is far easier to prevent these problems than it is to cure them.