Thrush Diagnosis and Treatment

Most cases of thrush occur in inactive horses that live in stalls. Unfortunately, this describes a huge percentage of horses in the United States, since over the past few decades horses have become ‘apartment dwellers.’

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Despite good hoof hygiene and exercise, horses sometimes get this unpleasant condition; rapid recognition and proactive management can prevent deeper damage.

You’ve seen it many a time–a horse gallops across a field and dirt clods fly every which way. With normal activity, your horse’s hooves are subject to a natural cleansing process that scours the bottom of the hoof and removes debris collected there. Any reason for inactivity, such as lameness or constraints on exercise and turnout, can influence how successful the natural cleaning action is that comes with moving across dry ground. It doesn’t require a fast run to accomplish this; even just regular movement at a walk and trot will be beneficial.

Bill Moyer, DVM, department head of Veterinary Large Animal Clinical Sciences at the College of Veterinary Medicine and Biomedical Sciences at Texas A&M University, has had a special interest in equine foot health for decades. He stresses, “Most cases of thrush occur in inactive horses that live in stalls. Unfortunately, this describes a huge percentage of horses in the United States, since over the past few decades horses have become ‘apartment dwellers.’ As a result they may be standing in any number of different conditions, yet the foot isn’t flexing and so doesn’t get the opportunity to self clean.”

The nature of your horse’s environment impacts the health of his hooves to some degree. Certain conditions and environments predispose the frog to bacterial or fungal infections; horses live in the presence of manure and soil where potentially destructive organisms proliferate, particularly if dirt and debris remain trapped in the crevices or grooves (sulci) of the frog. Pads also tend to trap moisture in the bottom of the foot and facilitate such bacterial or fungal growth. While poor hygiene can set the stage for development of thrush, even with the best of care infection can develop in the frog or sulci of the frog if conditions are excessively moist. Horses in the western United States don’t tend to have nearly as many–or as severe–thrush infections as those living in damp parts of the United States. Moyer can’t overstate the importance of activity enough, saying, “I have seen thrush in some of the best-cared-for and -managed places, but the common denominator is that it develops in horses that live ‘in.’ ”

Moyer notes, “Susceptibility to develop thrush varies with the configuration of the foot. A foot with an upright heel and deep crevices is a foot that is a real setup for thrush.” When the heels are high, the frog becomes recessed below the heels of the hoof wall, debris accumulates, and disease results. Horses with a chronic lameness condition that causes heels to contract and/or limitations on exercise are also primed to develop thrush, as are horses with unproperly trimmed heels. Moyer has noticed that while some affected horses have deep crevices of the frog, in other cases there is no depth to the frog clefts at all. He says, “My impression is that the incidence may be higher in Draft breeds than in light horses, mainly due to the nature of their feet with a deeper cleft that is more likely to retain moisture, which becomes the media for bacterial growth.”

What Does Thrush Look Like?

The consistency of a normal frog is much like that of a rubber eraser: firm, but pliable. Normally, the central sulcus is fairly shallow. In a horse that has limited exercise, and/or other hoof health issues, this central sulcus can deepen. If the crevice deepens, the tissues within have limited access to air and–especially if debris becomes lodged there–infection can develop, evident as a black and pasty discharge and often having an offensive odor.

A thrush infection usually is fairly superficial in its invasion of the tissues. Initially, it might be difficult to identify the presence of thrush, since in the early stages the horse is not lame and might show no other clinical signs. A more deep-seated infection can penetrate even further and, thus, move closer to sensitive tissue and potentially involve the digital cushion or other critical tissues. This can pose a real risk to the horse. In such cases, a horse can become lame and resent probing or squeezing of the tender heel and frog areas affected by thrush.

A severe form of thrush with substantial tissue damage might be confused with another condition called canker. Moyer describes canker as an explosive form of granulation tissue that tends to outgrow its blood supply, leading to a particularly noxious odor. The tissue that looks like spongy, rotten cauliflower is fragile and bleeds easily with finger pressure. Presently, no one knows what triggers canker.


An ounce of prevention truly serves as a cure when it comes to hoof cleanliness and health; regular turnout or exercise is essential. Moyer states, “Thrush is a disease that could have a much-lessened incidence if people would allow horses to be horses and to be outside, moving. The horse is so dependent physiologically on motion to circulate blood through their limbs; confined living conditions set them up for problems like thrush.”

As you pick out your horse’s hooves daily, inspect carefully for abnormal changes. Moyer comments, “Owner and/or farrier recognition of a foot that may be susceptible to thrush can go a long way toward avoiding infection. The frogs should be trimmed in a way that while clefts may remain somewhat deep, the frog isn’t allowed to grow to a point where it is overlapping. This keeps the clefts open for self-cleaning as the horse walks and frolics in turnout.”

Moyer notes that in the vast majority of thrush cases, an owner isn’t even aware that a problem exists and it is the farrier who is the first to recognize a problem.

Moyer has noted another possible reason for development of thrush, saying, “Some cases are potentially created by people through overly aggressive use of a hoof pick. I have seen cleaning that is rough enough to reach to fairly sensitive tissue, even to the point of bleeding.” While daily use of a hoof pick is to be encouraged to keep the frog sulci open and clean, he urges common sense and judicious care when using a pick.

Another main strategy is to keep your horse’s environment clean–daily mucking of the stalls and paddocks is important. All living areas should have good drainage, including pastures used for turnout. Try to limit your horse’s access to areas that could become simmering soups of bacteria.


The specific organisms that create such damage are not particularly easy to identify. As Moyer points out, “The problem with trying to culture these feet is that you end up culturing the barn.” A main objective is recognition; once the problem is identified, steps can be taken to eradicate the infection and to prevent recurrence.

The horse with thrush should be housed in a clean, dry area. Having the foot trimmed is essential. Daily inspection and cleaning of the hooves is critical to successful resolution of the infection. Effective treatment for thrush relies on generous removal of affected and infected frog structures with a hoof knife and nippers, along with thorough cleansing of all crevices. Vigorous use of a wire brush helps to scrub away all necrotic material.

Most thrush organisms are extremely susceptible to antibacterial solutions such as tamed iodine and bleach. Moyer believes that a dilute solution of iodine works as well as anything for disinfection of thrush-affected tissues. He recommends cutting regular iodine, such as Lugol’s, with water to a 2% solution. He says, “I like to administer it through a ketchup squeeze bottle that directs the iodine specifically into the frog crevices.”

Moyer cautions against applying a philosophy of “if a little bit helps then a lot more is that much better.” He remarks, “Many substances, including iodine, are caustic materials that can cause a chemically induced dermatitis if it drains onto skin above the hoof. What might have helped clear up the thrush problem with a couple of treatments might then turn into another problem due to a ‘too much’ or ‘too often’ approach.”

In some cases, it might be beneficial to treat the horse with poultice bandages and/or to implement daily foot soaks with antiseptic solutions. Moyer stresses, “While iodine is one of the world’s greatest disinfectants, it’ll only work for a short period of time if the foot remains continually exposed to the same thing that put the infection there. If the foot is very involved, as, for example, if the frog is so degraded that it peels away, then foot bandages should be used to protect the foot from the environment until the infection clears up.”

He has found diapers to be useful as part of a foot bandage since they “breathe.” Moyer also suggests that hoof boots can protect the affected areas, but he has concerns that these don’t breathe, while at the same time the foot continues to sweat, keeping the area damp–this is counterproductive to treatment.

Moyer also points out, “It is really worthwhile for the person managing a thrushy foot to wash their hands after treatment and/or to wear latex gloves. Take care to scrub under fingernails as well, as you don’t have any idea what has contaminated your hands. This is a good precaution in all cases, and even more important if the handler has an open wound.”

If a horse’s foot develops a bad smell, the frog feels “funky,” and/or if the horse exhibits lameness, you should call your vet. Moyer urges, “A veterinarian must be involved as soon as possible if there is any hint of complications. Even if the horse seems comfortable, there may be deeper tissue involvement that an owner may not be able to identify. Veterinary intervention is necessary to remove affected tissue to allow healing.”

You can check the degree of discomfort your horse is feeling by watching him on the longe line for lameness and by using your fingers to push on various structures on the bottom of his feet to check for soreness. Timely intervention is important so the infection does not invade deeper tissues, such as the frog and digital cushion between the heel bulbs. There is the potential for a persistent case to develop extensive degeneration of these structures, leading to instability of the heel bulbs or a sheared heel condition. If your hands are able to move each heel bulb independently of the other, this is typical of sheared heels. Such loss of support and stability in the rear portions of his foot can be quite painful for a horse, causing varying degrees of lameness. It takes time for the hoof to grow out, the supportive structure to be restored, and for soundness to return. It might be advantageous to apply a special bar shoe to hold the heels in stable position while the hoof grows and the infection is resolved.

Take-Home Message

Thrush is an infection of the frog and associated structures in the hoof. Regular exercise and good hoof hygiene are important to prevention and treatment. Owner observation, rapid recognition, and proactive management can avert the development of deeper tissue infection and the need for associated medical care.


Written by:

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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