We ask a lot of four bits of toenail carrying 1,000 pounds plus of lively animal, frequently with an additional 120 to 300 pounds on its back. Luckily, hoof horn is made of a highly modified, specialized, and tough material called keratin, a fibrous protein common to hair, fingernails, and rhinoceros horns. Keratin is produced by the coronary band at a rate between six and 10 millimetres (.25 and .40 inches) per month; thus, it takes between nine and 12 months to grow an entirely new hoof. Growth rate depends on a number of factors including:
Age: Foals’ and yearlings’ hooves grow fastest, about 12-15 mm per month; mature horses, as noted above; and aged horses, about six mm per month.
Breed: Some breeds tend to grow thicker, stronger hoof horn than others. Arabians, for example, are known for their dense, hard hoof walls, while some Thoroughbreds produce more fragile horn. There is tremendous individual variation within any breed, however.