my colt had rain rot, and that is what it sounds like you horse has. i would get some M.T.G from you local supply store, and it will clear it right up, you can also put it on their mane and tails to make them long and thick! good luck!
~A truly Fancy Pirate-Pirate-By All Time Fancy-Bay overo yearling.
~Mia-6 year old Thoroughbred mare. Ex polo Pony