A horse wears shoes for very nearly the same reason you wear shoes—to protect its feet from injury and wear. A horse’s shoe is a metal plate that fits around the outer edges of the hoofs to help give the horse better footing and keep the hoofs from splitting on hard roads.
The metal shoe is held in place with horse shoe nails. But since the nails go only into the horny hoof, this does not hurt the horse at all. Work horses wear heavy shoes with cleats to prevent them from slipping when pulling a heavy load. Race horses wear light shoes that can wear out after a single race.–Dick Rogers