Equine canker is an uncommon but serious problem that can affect a horse’s foot. Thrush is a bacterial infection that affects the horse’s frog and causes a black, foul-smelling discharge and results in deteriorated tissue. Although canker is also an infectious process caused by bacteria, it causes abnormal growth of tissue in the frog that resembles off-white cauliflower in color and texture, so these conditions are very different even though canker can also have a foul odor. Lots of folks assume their horses have thrush and treat for it when canker is the real problem. Thrush treatment will have no effect as canker needs to be treated with surgery.
Although canker can be diagnosed on clinical appearance, sometimes a biopsy is needed. The infective and proliferative tissue must be surgically removed with a scalpel blade. The procedure can be done while the horse is standing after numbing the foot with a local anesthetic and applying a tourniquet to control bleeding. After removing the infected tissue, the surgical site should be frozen with cryotherapy to remove all adjacent surface bacteria. Then the veterinarian will apply an astringent dressing with antibiotics and bandage the foot until the tissue is cornified and healed. It is critical to keep the foot absolutely dry, so the horse must be kept in a dry covered stall with shavings that will absorb moisture. Although we do not know the cause of canker, Dr. Steve O’Grady indicates it does not appear to be caused by unsanitary conditions as most of the horses he sees with the condition are well managed.