Scratches affects the backs of the pasterns and bulbs of heels and is most commonly found in horses exposed to moisture for long periods of time, whether from standing in a muddy field or a wet stall. Constant moisture can become an irritant as it penetrates delicate skin, causing inflammation, redness, and ulcerations. When coupled with muddy or dirty surroundings, it can be an ideal situation for invasion of bacteria and fungi. Mild cases are usually amenable to simple cleaning and topical treatment. In severe cases, or if the leg becomes hot, swollen, and painful, it is a sign that the infection has become more serious. In such cases, it is important to consult with your veterinarian.
Regardless of the underlying cause, most cases of scratches benefit from the following management. Start by clipping the long hair from the affected skin in order to make it easier to keep clean and dry. Next, wash the area thoroughly but gently, making sure to remove dirt but being careful not to aggravate the skin. A single cleaning with an antibacterial soap such as Betadine scrub is appropriate, but the skin should not be subjected to repeated treatments with harsh cleansers or disinfectants. Follow by lightly towel-drying the area. If scabs and crusts are present, try to soak or sweat these off rather than picking them, which seems to aggravate the inflammation.
Limit your washing sessions to only once a day as additional moisture could further inflame the area. Also, try to keep your horse out of muddy or wet places and make sure that his bedding is clean and dry. In the future, avoid hosing your horse's fetlocks and pasterns, unless you have a specific reason, and always make sure to completely dry the area afterwards. You should thoroughly clean any hobbles, boots, or wraps before you use them again.
For mild cases, cleaning as above followed by treatment with a modest amount of Corona ointment is helpful. This ointment is not water soluble and can attract dirt, and shouldn't be used if the horse is turned out on a dry-lot or anywhere muddy. It is very useful if the horse is kept in a stall during treatment, as it keeps the skin soft making it less likely to split open as the horse walks. More severe cases often require topical treatment with cream that contains both antibiotics an antifungal agent, and dexamethasone to reduce inflammation. Really severe cases often benefit from a course of treatment with oral broad-spectrum antibiotics.