Farm Forum

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.

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 urbanized. 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.

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 overgrown hooves.

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. If debris becomes lodged there infection can develop, evident as a black and pasty discharge and often having an offensive odor.

Identifying and treating thrush

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. Canker is 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. 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. 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 runs around. 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.


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 dilute iodine and bleach.

In some cases, it might be beneficial to treat the horse with poultice bandages and/or to implement daily foot soaks with antiseptic solutions. While iodine is one of the world’s greatest disinfectants, it will 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.

Diapers can be a useful part of a foot bandage since they breathe. Hoof boots hold in the sweat from the foot, keeping the area damp and contaminated.

If a horse’s foot develops a bad smell, the frog feels decayed, and/or if the horse exhibits lameness, you should call your vet. 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.

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or