From: Bobbie
Two years ago I bought an aged mare (16), and brought her from the ranch where I work in the summer (in Wyoming) to my home on the Mississippi Coast. It was in the fall of the year - the mare was fine. The following summer she broke out in a rash which my veterinarian diagnosed as "rain-rot". (In Wyoming we have from 5 to 11 inches of rain a YEAR. In Mississippi we can have that much in a couple of days.) That first summer the rash was not so bad that we couldn't ride her (primarily on her chest). Last year it started again as soon as the weather was warm. It was so severe that her mane, forelock and most of her tail hair fell out. The sores were all over her body, oozing serum, making it impossible to saddle her. It reached a point where my son (who keeps her for me in the summer) was considering putting her down. He treated her with everything suggested, finally cortisone and the rash began to disappear. However, it was September, and we don't know whether the medicine helped her, or the cooler weather.
Another veterinarian said that the horse had never built up an immunity to all the flies here, and also was allergic to everything! Her diet is 12% pellets and coastal bermuda (grass) hay.
She is a wonderful, old mare, perfect for my grandchildren, surefooted, bomb-proof (been there-done that) a tough old mountain horse. Hadn't thought of this before - could the change in altitude (from 10,000 feet to sea level) have any bearing on this problem?
Bobbie McIntyre
The usual signs are little (often 1/4" across) clumps of matted hair anywhere (or everywhere) from the horse's neck across his back to his croup. When you groom the horse, you'll find that the matted hairs are sticking to, or through, a small crusty scab, and that when you pull the scab away, the hairs come with it, leaving a damp red open spot in the skin.
The particular bacterium involved here is Dermatophilus congolensis. Sunlight will kill many bacteria, or render them dormant, and in the summer when there's lots of ultra-violet light and the horses have short coats, rain rot is not so prevalent. Outbreaks are much more common in the winter or wet season, when longer coats can hold moisture close to the skin, and the sun is often absent or feeble, quite unable to reach the bacteria through a thick, damp coat. In your particular case, since you've moved from a dry sunny high-altitude location to a damp, cloudy, low-altitude location with LOTS of external parasites, the location is almost certainly a factor.
Rain rot is spread from horse to horse. Horses can share this with each other directly -- in pasture, say -- or by way of an intermediary such as certain biting insects. But this disease is also, very often, spread by horse OWNERS -- if they use the same brushes, saddle pads, or tack on multiple horses. It's a compelling reason for horse-owners to use a horse's equipment on that horse ONLY, and to keep everything very clean. My apologies to those horse owners who learned everything they needed to know in kindergarten, but SOMETIMES SHARING IS A REALLY, REALLY BAD IDEA.
There are horses that carry the bacteria all the time, but don't show visible signs -- their hair coats look normal. But if they are carriers, the bacteria can easily be spread from these horses to other horses that WILL develop the clinical signs of the disease -- so, once again, even if all your horses seem quite normal, each horse should have his own personal equipment.
The treatment varies according to the cause and severity of the horse's condition. You must work with your veterinarian to do what's best for your horse -- your vet will be able to diagnose the problem, evaluate its severity, make a very good guess at what caused it, and tell you exactly what YOUR particular horse needs, and for how long, whether it's merely a week of daily medicated baths and rinses, or whether antibiotics are called for as well. There are OTHER skin diseases that horses can get -- some bacterial, some fungal -- and you need to be sure of the disease before you can treat it appropriately.
The usual treatment for rain rot is vigourous daily grooming to remove the crusty scabs and infected hair, followed by a bath with medicated shampoo (your vet will tell you which one to use). Often, your vet will suggest that you follow the medicated bath with a providone-iodine rinse that will stay ON the horse until you give it its next bath (the next day). In many cases, a week of daily baths and rinses (and don't forget to clean the grooming implements daily, along with the horse!), followed by several weeks of twice-a week baths and rinses, will take care of the problem. Again, you'll need to work with your vet. If your horse is badly infected, he may require bathing more than once a day, and he may find the grooming process very painful, as the tools come into contact with the ulcerated skin under the scabs. Some horses with severe rain rot may require sedation before they can be groomed with the vigor that's required to remove the crusts and hair.
If you are treating an infected horse, be extra-careful to clean everything that is touched by the horse. Before you use a halter, bridle, blanket, or any other piece of equipment on another horse, clean AND DISINFECT it. The same goes for all grooming equipment -- including things that you might not think to disinfect, such as mane combs, scissors, and clippers. If you turn an infected horse out on pasture for the summer, the sun will do him good, but be sure to clean and disinfect his stall -- or those bacteria will be there waiting for him in the fall. Your vet will be able to give you the best advice on how to disinfect your horse's stall, stable, or shed.
Jessica
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