You are probably referring to "rain rot," also known as "rain scald," "dew poisoning," or "mud fever." This condition occurs most commonly under damp conditions (but not necessarily) and is caused by an Actinomyces microorganism. These microbes have characteristics of both bacteria and fungi and cause scabbing and oozing of serum from the skin. These microbes can be spread from horse to horse by using common tack and equipment without thorough cleaning and disinfection. The best treatment is usually frequent bathing with a shampoo containing an antimicrobial such as betadine or nolvasan. If the condition persists after several such baths, you should call your veterinarian for alternative treatment options.

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