Of our many domesticated animals, horses are one of the few that wear shoes. Wild horses, however, seem to get along just fine without iron footwear. So why do we strap shoes on tamed horses?
A horse's hooves are perfectly adapted to the horse's natural habitat. Like human fingernails, the outer part of a hoof is made of keratin, a tough material that lacks nerve endings. The absence of nerve endings is why clipping your fingernails and nailing on a horseshoe doesn't hurt. The hoof surrounds the sole, a tough patch of skin that when properly balanced with the hoof supports the horse's weight without bruising. Near the back of the sole is a bulb of spongy, insensitive material called the frog, which functions as the hoof's shock absorber.
In the wild, unshod hooves grow downwards approximately two-tenths of an inch per month. A wild horse's natural daily activities, however, wear away the hoof at roughly the same rate, maintaining the proper balance between hoof wall and sole. The rate at which hooves grow depends on the breed of horse and its habitat, but the natural balance of growth and wear works across breeds.
Wear and Tear
Since many domesticated horses are made to walk and run on hard surfaces such as roads and dirt paths, horseshoes are necessary to keep the hoof wall from wearing away too quickly. Without protection, the hoof would quickly wear down, disrupting the balance between hoof and sole. Without the aid of the hoof, the sole and frog may become damaged. But since horseshoes don't allow for natural wearing away, shod hooves must be regularly trimmed to maintain a balanced state.