The main composition of horns is keratin, the same material that makes up hair and fingernails. The core of a horn is, however, made of bone.
Used for defense, horns are extremely advantageous in the wild. Horns will grow for an animal’s entire life, much like a turtle’s, which is also permanent and comprised of bone and keratin. But horns cannot grow back, which means a broken horn can make an animal extra vulnerable in the wild.