The wet weather of fall and winter can lead to rain rot (also called rain scald). There are other causes of bumpy, scabby skin, too, including a hypersensitivity reaction or a bacterial or fungal infection. If you notice such areas on your horse’s coat, notify your veterinarian. He or she may recommend a broad-spectrum antimicrobial shampoo that will kill any bugs. To be most observant, groom daily, following a set pattern that assures you check over your horse’s entire body.