Equine snowshoes do exist. They're generally either hoof shaped or square and used to be made of wood. They were invented for logging in winter in Canada and the Midwest. (And are often attributed to Paul Bunyan).
Early snowshoes strapped to the hoof with leather. Later ones were actually attached to the hoof.
The snowshoes would not just increase the horse's ability to pull in deep snow but also prevent snow from balling in the hoof, which can make a horse slip (and annoy them).