A: Canker is an infection that invades the surface tissues of the hoof and causes overgrowths, beginning in the frog and extending to the sole and hoof wall, and in severe cases even to the skin of the pastern.: I'm curious about the hoof condition known as canker. I was told that my older horse had it after I noticed a smelly discharge that started during a spell of wet weather. I haven't been able to find a lot of information about canker, and my farrier and veterinarian have never treated a horse for this.