A recent post at FHOTD prompted me to explore the Gentle Giants Draft Horse Rescue website this afternoon. Over the past two years this impressive organization has been forced to euthanize two horses suffering from canker. I'd never heard of the condition before today, but it makes founder rehab look like a walk in the park.
The veterinary community is somewhat flummoxed by canker. Everyone agrees that it's caused by a bacterial infection that initiates abnormal keratin production, but no one can predict which horses might be affected. The draft breeds are definitely more susceptible, possibly due to concussive weakening of the hoof structure and its immune function. Factors like age, working history, stable management and metabolic condition seem unrelated to canker risk, and veterinarians have never been able to recreate the disease under controlled conditions.
Keratins are the structural proteins that make up human fingernails and horse hooves. Once a cankerous infection is established excess horny material begins to push up through the frog. If the condition goes untreated it will move on to the soles, bars and heel bulbs. There is no sure-fire cure for canker, but surgeries that excise all of the infected tissue seem the most effective (in combination with months of diligent care, of course). Most sources make it sound like a death sentence, and my hat goes off to those rescuers at Gentle Giants for their dual heartbreak.