Just to add. In thoroughbreds, the bones are very small down around the hoof. There is little muscle mass down close to the hoof and up about 12 inches. So if a break occurs in that area, the blood supply is limited , and healing takes longer. Dogs and cats have more muscle mass along the bone and heal better as a result of this. Also, horses are very heavy being support by these narrow bones, take one leg out of the equation and the other legs give out as well.
Hope it helps