The horse was probably crippled up pretty bad, and they were wanting to make it easier for it to break over it's toe. Is part of the shoe thicker than the other part? I expect they didn't want it's heels sinking down. When the round shoe was used, the horse was probably not in any shape to ride or drive. Personally I've never used a round shoe, and don't know a lot about them, except I know they are used in certain situations to help bring a horse sound for use.