Horses don't have feathers...right?
Actually, depending on the breed, they do. Feather is long hair that covers a horse's lower legs and hooves. It is seen in draft breeds and also in cobs and most of the "native" northern European breeds.
Feather is seen on horses that are adapted to cold weather, so its purpose is probably just what you would think - to keep the horse's feet warm.
Some people trim feather off. It's most common to do this if a horse only has a little bit of feather - sometimes pony crosses or draft crosses may have just a bit of straggly hair at the back of their leg that generally doesn't look good. Others trim it off in summer when it's warm and let it grow in winter.
Draft horses are supposed to have feather and draft show grooms spend a lot of time brushing it out and sometimes washing it (especially on Shires and Clydesdales, that generally have white legs) to make it look perfect.