Welcome to the wonderful world of Clydesdales. It sounds like your horse has a case of scratches. Very prevelent in clydes, Shires and Gypsies. It is an ongoing battle. Ask your Vet, ask the local vet university, ask anyone, You will get a different answer from all. My remedy, was wash and scrub his legs, I used iodine soap, let feet dry about 10 min till water doesn't drip anymore, then srpay with a bottle of Frontline spray, you get it from the dog vet. One bottle does about 2 applications, 8 legs on a draft. That is just the beginning, if it gets worse there are medications that can be given. I used the prescriptions given to me by the vet from the Anheuser-Bush Clydesdales. And it was still a constant battle.