I need help with my horse; he has . . .
I had a friend whose horse had this problem, and she scrubbed the spots with Head and Shoulder shampoo. Don't know if it was what helped or not, but the spots did go away. Also, could be a fungus or bacteria--there are fungal and bacterial shampoos available, but you'd have to shampoo him every day for a week to get rid of it--it's very difficult to eradicate. Might also be a skin parasite--try an ivermectin wormer.