Most horse people have dealt with problems with their horse’s hooves. One of the more unusual conditions that affect the frog, bars, and sole of the foot is called “Canker.” Once thought to be cancerous, veterinarians have since determined that canker is an anaerobic infection in the superficial epithelium of the hoof (the outermost tissues, which produce the horn like hoof exterior.) It's unknown what bacteria causes canker and how it begins. But. it has been suggested that the Bacteroides species, (the same bacteria which causes "foot rot" in sheep,) is the culprit.
Equine canker can affect any horse or pony of any age. It is normally found in the southeastern United States, but cases have been diagnosed throughout the U.S. Sometimes mistaken for thrush, it is actually relatively rare and unlike thrush, (which destroys tissues in the foot,) canker creates abnormal tissue growth. One significant difference is that while thrush may eat at tissue, the inner tissues of the digit are protected until bacteria invades deeply enough to damage the more sensitive internal structures. Canker, on the other hand, spreads in live tissue, without the help of oxygen.
Canker begins when the invading bacteria triggers abnormal keratin production, or overgrowth of the horn. This is found predominately underneath the horn as the infection spreads throughout the epithelial layer. When looking at the hoof of an affected horse, you will notice light colored, moist spongy matter appearing in the grooves on either side and in the center of the frog of the hoof. (Often described in appearance as looking like cauliflower.) In very bad cases where there is extensive infection, heat might be felt in the hoof, but this is uncommon.
The cause of canker is currently unknown but is thought to be associated with poor quality bedding and housing. However, it has been found in horses living in immaculate barns. It appears from studies and review of the incidence of cases that stalled horses with little exercise seem more predisposed to the disease than horses that are either exercised regularly and/or kept outdoors.
In a recent study, a group of researchers found spirochete (spiral-shaped) bacteria present, similar to that found in cows and sheep with digital dermatitis. In cows and sheep, this problem is also associated with poor quality hygiene.
As we have determined that poor bedding conditions leave a horse more susceptible to canker, it's important to ensure your horse is kept on clean, regularly mucked out bedding to reduce their risk of contracting the infection. Treatment of canker can be difficult, but, there are treatment methods available.
1. “Superficial debridement” or the cutting away of abnormal tissue over the entire affected area is one method of treatment. The Veterinarian would need to give a general anesthesia or a nerve block in order to carry out the procedure. Only the superficial layer should be removed as taking away deeper tissue could result in long term damage to the foot. There is also a chance that the infection can spread into deeper tissues. Some veterinarians follow the debridement with two to three superficial freezes of the affected area to further kill off the diseased tissue.
2. It is very important to keep the horse’s bedding as dry and as clean as possible as Canker thrives in moist conditions.
3. Your veterinarian may prescribe topical treatments. The two most effective topical therapies are the antimicrobial drug metronidazole, applied as a ground powder to the area, and 10% benzyl peroxide solution. These should be applied on gauze pads.
Different horses have varied responses to treatment. Some cases heal within a week, while others can take months. Aggressive treatment during a 10 day period should be sufficient to eliminate the canker. Once the tissue has healed, it is very rare for the disease to recur. However, if allowed to take hold before healing is complete, canker may return.
*Image courtesy of Dollar Photo Club
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