Thrush Prevention

Thrush is a very common word for those of us who have been spent any amount of time around horses. It is one of the more common diseases of the equine hoof. But does everyone know what thrush is? How do you prevent it, or how do you treat it once it has set up shop within your horse's hooves?

Michael A. Ball, DVM

Thrush is characterized by a thick, black discharge.

Thrush is a disease of the foot that usually occurs within the frog (the wedge-shaped structure on the bottom surface of the foot) and its sulci (the grooves next to and in the middle of the frog). The disease is characterized by a very soft frog and sulci. When the frog is picked out, a thick, black discharge is present that is easily removed from the sulci. There also is a characteristically pungent odor. Once smelled, it will never be forgotten, and you have your diagnosis.

The disease is thought to be caused by a bacterium. Usually thrush does not cause lameness if the disease stays in the superficial external and non-sensitive area of the frog. However, if left unchecked, the disease can extend into the sensitive tissue of the frog and make horses quite sore. They might flinch as you clean the sulci. Thrush can progress to a severe lameness that can be seen at a walk--much like a hoof abscess. The infection in general leads to degeneration of the frog. Thrush also can cause enough degeneration of the frog that portions of that structure have to be removed by your veterinarian or farrier.

Thrush is most commonly associated with poor management practices or conditions. It can be seen in horses which are allowed to stand in paddocks or stalls that are full of wet manure, or just in horses which do not regularly have their feet cleaned. However, this disease is also seen in horses which are never allowed to stand in manure.

Thrush can also occur in horses, for example, that wear full pads underneath their shoes. The full pad is good because it will protect their feet from rocks or help absorb shock in order to prevent lameness. On the other hand, the full pad does not allow the hoof to be cleaned on a regular basis. As a result, shavings, straw, or dirt, but most importantly moisture, get trapped underneath the pad and stay there for six to eight weeks--until the shoes are reset. As a result, this long-term exposure to moisture and bacteria sets up the perfect environment for thrush to thrive.

I am not saying don't ever put full pads on your horse's feet. I am just warning that if your horse develops thrush after wearing full pads, he/she might need to have the shoes reset more frequently than the usually recommended six to eight weeks. If the disease is mild, the feet can be treated for the thrush while the shoes are being reset. Basically, horses are at risk for developing thrush in any condition where the bottom of the hoof is kept in a damp environment.

How can you prevent thrush?

It's simple. Keep your horse's feet clean. Every time you groom your horse or before every ride, you should pick out the feet. Don't forget to clean the frog and the sulci--don't just remove the shavings or dirt trapped in the sole. This is an excellent practice not only for preventing thrush, but also in checking for any foreign objects that might have found their way into your horse's foot, such as nails or rocks. So, you can prevent several potential problems with one hoofpick.

Also, try to keep your horse's stall or paddock as clean and dry as possible. If you live in an area like I do--Central New York state--it is impossible during the months of March through June to have anything short of a mudslide in your paddocks. But daily foot cleaning will help offset the otherwise muddy conditions and will go a long way in helping prevent thrush.

What do you do if you find the hallmark signs of the disease in your horse's feet? First, clean the feet. Make sure you have removed as much of the black discharge as possible. Then, allow the feet to dry. There are a number of commercial products that are available to help dry the feet and rid the foot of the infection. Some examples are Kopertox, or Thrush Buster. Other medications can be used such as a dilute bleach solution, tincture of iodine, or a 10% formalin solution. These solutions can be applied topically to the frog to help resolve the infection (watch your clothes; most of these products will stain them forever). Wearing gloves to protect your hands is a good idea.

Be careful though. Overzealous use of these products can damage the frog by drying it out too much. In addition, most of these chemicals are strong tissue irritants and are very capable of causing chemical burns of the frog and skin if used in excess. The thrush may be long gone, but the foot remains quite sensitive from the chemical irritation of the treatment--use these products as directed and don't overtreat. Also, avoid getting these products on the coronary band and soft skin area of the pastern. If you don't think you are making headway with the infection within a few days, contact your veterinarian. There might be another problem brewing within the hoof.

Thrush Or Canker?

There is another disease of the hoof which can be confused with thrush. This disease is called canker, which is why you should have your veterinarian out to check your horse if you don't get resolution of the supposed thrush infection quickly. Both of the diseases primarily affect the frog area, at least in the beginning. Canker more commonly affects draft-type horses, although it has been seen in light breed horses. Canker also has a very foul odor that accompanies the disease similar to that of thrush. So, the unfamiliar can be fooled. The difference between thrush and canker is that with canker, the tissue in and around the frog is not destroyed, but proliferates (grows excessively).

The cause of this disease is unknown, and although secondary infections of the hoof usually occur, a purely bacterial origin has not been proven. Left untreated, the disease can become extensive, and it can distort the hoof quite dramatically. These two diseases also are treated a bit differently, so early distinction between the two is important.

Canker usually is treated by removing the abnormal tissue, either with the horse standing or sometimes under general anesthesia if extensive debridement of the hoof tissue needs to be performed. After the abnormal tissue is removed, aggressive topical antibiotic therapy is instituted. One of the most important aspects in treating this disease is keeping the hoof in a clean and dry environment. Therefore, the foot often will need to be kept in a bandage for the duration of the treatment.

More On Thrush

What if you examine the hoof and the entire frog is unhealthy or perhaps even loose? For these cases, your veterinarian and/or farrier needs to get involved. A hoof pick just won't do the job. The diseased frog will need to be removed along with any other unhealthy tissue with a sharp hoof knife. Sometimes a bar shoe will be recommended to give support to the much smaller frog after the tissue is removed. However, these cases are not very common.

If you are having trouble resolving the infection or if your horse is lame, please consult your veterinarian. He or she can confirm whether or not your horse has thrush and recommend further treatment if necessary.

About the Author

Christina S. Cable, DVM, Dipl. ACVS

Christina S. Cable, DVM, Dipl. ACVS, owns Early Winter Equine in Lansing, New York. The practice focuses on primary care of mares and foals and performance horse problems.

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