Why do horse hooves continue to grow throughout life?

Horse hooves, like the nails and claws of other mammals, are composed of the fibrous protein keratin. They grow continuously throughout the animal's life from living cells located at the base, or attached end, of the hoof.1

This constant growth is a natural biological process, and the length of the hoof is typically regulated by the wear it experiences as the animal moves. Because horses—which are perissodactyls—walk on the tips of their single digits, their hooves serve as a durable, protective covering that bears the weight of their bodies. In domestic settings, horseshoes are often applied to the hard outer portion of the hoof, known as the unguis, to provide additional protection against breaking and splitting.1