I did not want to derail @CmonBobby's fascinating thread so hope no-one minds if i start my own.
This is more a question DH keeps asking me. What happens to the hooves of wild horses? Why do they not grow and curl up and eventually cripple them like we often see with neglected domesticated horses. I always sort of whitter vaguely about the constant movement along ground wearing the hoof away but truth is i'm not sure.