This mare's thick, wet coat may lead to rain rot.

Rain rot. We all know what a nuisance it is, that bumpy skin infection caused by Dermatophilus congolensis. This “bug” thrives in high-moisture, low-oxygen skin conditions that occur under the winter coats of horses that get wet, or in horses with lighter coats when blankets get soaked through. Under these conditions, any horse can develop the problem, but it’s likely to be more severe and more common in horses with weak immune systems.

The infection is easy to miss in the early stages unless you are regularly checking and grooming your horse. It begins as areas of tiny scabs that feel like small bumps in the coat, but it’s not easy to see when the coat is dense.

At this stage the horse isn’t sensitive to touch, but may be to grooming or if you tug on the hairs attached to a scab. Scabs come off with the hair attached, leaving a small raw area in the skin. If undetected at this early stage, areas of infection will grow and coalesce, forming thicker and thicker scab crusts. In advanced cases, the large crusts form visible bumps in the coat, with tufts of hair sticking out of them. The horse may shrink away from even a light touch.

Air and sunlight are the natural enemies of this organism, but they’re effectively shielded by the heavy crusts. Effective treatment means removing the crusts and treating the skin with a product that will eliminate the organisms.

To begin, curry the horse lightly with a rubber curry comb or mitt. The horse’s skin is going to be sensitive, but do the best you can. This step will remove small scabs. Horses with dense coats will be easier to treat if you clip the area. This improves penetration of shampoos and sprays. Pick a product from our list that is appropriate for the level of crusting you have.

After allowing products to sit in contact with the crusts and skin for five to 10 minutes, gently scrub areas of crusting and remove as much as possible. Rinse, and dry the coat using towels and a hair dryer. Repeat the process daily until all crusts are removed and skin has healed over. Hair regrowth is usually rapid once the infection has been eliminated.

Keep the horse protected from rain and snow to avoid reinfection. If he does get wet, towel and blow dry the coat as quickly as possible. If after a week of treatment you’re not making good headway toward healing, or still finding new areas of scabbing, contact your veterinarian.