Rain scald, also known as rain rot, it a bacterial infection caused by the bacteria Dermatophiluscongolensis, which usually affects the back, rump and sometimes the face. The lower limbs of the horse can also be affected, this is called mud fever.
If your horse is subjected to prolonged periods of time in wet conditions the surface of the skin softens allowing the bacteria to invade the surface layer of the skin, causing infection.
Infected areas become scabby and the hair matted. When the scabs are removed the surface of the skin underneath will be moist and in severe cases raw. These areas will be painful for your horse and in cases where large areas are affected the skin will feel hard to the touch because of extensive scabs covering the area.
Rain scald on the lower limbs is known as mud fever and is usually complicated by complex mixtures of several different bacteria; there may be also be fungus organisms present. Mud fever is usually seen on the back of the pastern and fetlock, and as well as scabbing of the affected limbs, some horses become significantly lame and others may develop filling of the limbs.
As well as checking for the obvious signs of scabbing, hair matting and hair loss, your vet will want to take some samples back to the lab to test. Your vet will probably take some samples of the scabs and possibly a small sample of hair from the affected areas to check.
Any scabs, crusts and infected debris can be gently removed by using hot, we poultice dressings every 8 hours for a couple of days. The areas should then be cleaned with an antibacterial shampoo and dried afterwards. If possible, the horse should be kept stabled to prevent further skin wetting until the areas have healed.
Antibiotic creams may also be helpful.
Severely affected horses may also need antibiotic treatment either by injection or as a course of oral antibiotics.
Avoid turning your horse out for prolonged periods of time in rainy weather without a rug or appropriate shelter.
If you know your horse is prone to developing rain scald, it might be better to leave your horse stabled in wet conditions to avoid the problem completely.