Hair loss and lesions on the horse's skin are common and one of the most common is ringworm. Ringworm is not a worm but actually a fungal infection that is contagious between horses and these infections can be spread between horses by tack such as halters and saddle pads. Lesions can occur anywhere on the horse but I usually see them initially on the neck area. They appear as small crusted areas without hair and will sometimes appear in a ring pattern. Horses with ringworm may be itchy and will be seen rubbing the affected areas on the fence or stall. To diagnose ringworm, a fungal culture is required and this is important because other diseases look similar and require different treatments.
One of these similar diseases is rain scald. Rain scald is a bacterial disease that also forms crusts but the crusts are usually thicker than those with ringworm. Rain scald is caused by the bacteria Dermatophilus and is usually seen in the fall and winter. Your vet can diagnose rain scald by plucking some scabs from the skin and examining them under the microscope. Treatment of rain scald involves removing the scabs by soaking them with an antibacterial scrub and allowing them to soften. Some of these scabs can be tightly attached so some patience is required. The infection responds to penicillin injections or oral trimethoprim sulfa antibiotics. On the other hand, if ringworm is involved, treatment involves shampooing with an antifungal shampoo or lime sulfur dip, so contact your vet if your horse has a skin problem. Getting a correct diagnosis is better for the horse and less expensive for the horse owner than guessing at the diagnosis and buying an ineffective product at the feed store.