Hoof canker is an unusual condition in horses. The rare disease results from abnormal growth of the outer horn layer of the hoof
It typically originates in the frog, the bottom portion of the hoof toward the heel. In severe cases, canker can spread to the adjacent sole, hoof wall and bars.
Horses with canker may or may not be lame. The canker lesion is grey to pale tan and proliferative, resembling cauliflower or proud flesh, also known as granulation tissue. It can occur in one hoof or several on the same horse.
Canker is diagnosed based on the presence of the characteristic hoof lesion. In some cases, veterinarians may collect and submit a biopsy to a pathologist for supportive evidence of the diagnosis.
It is important to distinguish canker from thrush since they affect the same part of the hoof but re-quire different treatment. Thrush is characterized by tissue death and breakdown of the hoof, while canker features excess white tissue.
If a treatment for thrush isn’t working, then it may be a case of canker.
This disease has been well known for years. My 1921 copy of The Practical Stock Doctor provides this description: “As the secretion escapes to surrounding parts, it dries and forms small, cheesy masses, composed in part of the partly dried horny matter, exceedingly offensive to smell.”
The book emphasizes that certain breeds are predisposed to the condition—“heavy cart horses are more affected than any other class.”
Modern veterinary textbooks also suggest that draft and warmblood breeds appear to be more commonly affected. Middle age or senior horses may be more likely to develop the disease.
The cause of canker is unknown, but infection with bacteria and fungi is one possibility. More cases have been documented in summer and fall, but more research is needed to call it a seasonal pattern.
Some veterinarians suggest that muddy, unhygienic conditions are to blame. Some observe more canker cases in stabled horses compared to those on pasture.
There is also evidence to suggest that infection with a bovine papillomavirus may be the culprit.
New research published in the journal Veterinary Pathology sheds new light on cankers.
The researchers from Vienna, Austria, with a collaborator at the University of Edinburgh in Scotland, examined microscopic tissues from horses with canker and compared them to tissues from normal horses.
Using molecular markers that often help identify and diagnose cancer, the researchers found that cells were not proliferating excessively as was previously thought.
Instead of pre-cancerous overgrowth, the lesions of canker appear to arise from abnormal maturation of the cells that form the hoof.
The lack of the normal, hard outer layer allows the inner tissue layers to protrude, creating the proliferative, cauliflower-like appearance.
Researchers also found that the tissue changes of canker are similar to sarcoids (masses that arise in the skin of horses).
Many researchers have long suspected that a bovine papilloma virus is responsible for both canker and sarcoids; therefore, finding similar changes further supports the connection, although a definitive link to the bovine virus requires further investigation.
Treatment consists of removing the outermost layers of the abnormal horn, then keeping the hoof dry and clean with bandages. It can take several weeks for the normal hoof horn to regrow and the canker may require a few rounds of treatment to achieve a cure.
Some veterinarians advocate use of antibiotics directly within the defect.
Although canker is rare, early detection and treatment are im-portant for achieving the best prognosis.
It is important to examine hoofs regularly and if you see signs of hoof abnormalities within the bottom structures of the hoof, consult with your farrier or veterinarian.
Dr. Jamie Rothenburger is a veterinarian who practices pathology and a PhD student at the Ontario Veterinary College. Twitter: @JRothenburger