Vitamin A is not the only factor in susceptibility to rain scald. Funny, last year someone was swearing blind it was only lack of Vitamin E that caused the condition, and Vitamin E supplementation was the only real answer.
Like many infections, multiple factors are at work in susceptibility - dietary ones including Vitamin A, Vitamin E, selenium, and a whole bunch of other trace elements involved in immunity; environmental factors like humidity and moisture, and genetic factors. You can spread a rain scald infection by brushing with a sharp-bristled brush, which creates little scratches in the skin into which the causative organism is thus introduced. Take that brush to another animal and you may well set up another infection. While the organism that causes rain scald is pretty ubiquitous, getting it directly into skin scratches gives it a head start. One of the reasons the rear cannons on a horse are a typical place for rain scald is that the condition is spread by biting flies - who also introduce the causative organisms directly into the skin - past the protective layer which usually forms a physical barrier.
Regularly wash and disinfect brushes, saddle blankets, rugs etc that are in contact with a horse with active rain scald - hanging them out in the summer sun to dry gives these items high doses of UV, which also kills pathogens.
The reason Vitamins A and E are a big factor for this infection in many horses these days is that many horses are now stabled/dry yarded and fed mainly on dry feeds. The vitamin content of fresh pasture is higher than the same pasture made into meadow hay. Vitamins A and E are fat-soluble and stored in the body, so in the dry season, wild horses will draw on what they accrued during the growing season. Supplementing horses to make up the shortfall is common practice in performance horse stables.
Treatment is also most effective if it's multi-pronged. If your horse is dry fed, definitely give it therapeutic doses of Vitamins A and E (and any other things it might be lacking - a good mineral/trace element mix doesn't go amiss), wash it repeatedly with a medicated shampoo targeted at this organism (you can get these at veterinary surgeries - don't assume any "medicated" shampoo will be helpful) - make sure the scabby areas get a thorough treatment, and gently remove what you can. Clipping can help, but the horse will then need to be sheltered from the weather.
Rugging can help, if it keeps a horse drier to rug it - but never rug with a non-breathable rug (you can get winter rugs that are waterproof and breathable, like mountain climbers' jackets). In summer, light cotton rugs (or shady trees, if the horse is inclined to a midday siesta) might be good during peak UV, since the scabby areas are UV sensitive and can get sunburnt. While UV also kills the causative organism, and in that sense exposure is good, avoid exposing to the point of causing burns to the damaged areas. If it rains, a cotton rug will get soaked though and worsen the problem.
Are you in Queensland / northern NSW / NT? Here in WA, rain scald is rare in summer due to our dry summers. If you live in summer-wet areas, it's a prime climate for getting rain scald infections. But do you know, some Queenslanders on an Australian horse forum swore by Listerine mouthwash as a helpful tool in treating the condition. They put it in spray bottles and lightly sprayed the affected areas daily (on top of using medicated shampoos etc). You could give that a go as well. Good luck with it!
SueC is time travelling.
Last edited by SueC; 07-10-2015 at 08:27 PM.