Mange is caused by microscopic mites that invade the skin of otherwise healthy animals. The mites cause irritation of the skin and a hypersensitivity reaction, resulting in itching, hair loss, and inflammation. Mange is rare in horses. There are several types of mange that affect horses, including sarcoptic mange (equine scabies), psoroptic mange (mane mange), chorioptic mange (leg mange), demodectic mange, harvest mites (chiggers, trombiculids), and straw itch mites (forage mites).
Sarcoptic Mange (Scabies, Body Mange)
Although rare, sarcoptic mange is the most severe type of mange in horses. The first sign of mange is intense itching, caused by hypersensitivity to mite saliva and feces. Anti-itch medications do not help. The animal will rub and chew on its skin, causing sores and bald patches to appear on the head, neck, flanks, and abdomen. The sores start as small bumps and blisters that later develop into crusts. Hair loss and crusting spreads, and the skin becomes thickened. If untreated, the sores may spread over the entire body, leading to emaciation, weakness, and loss of appetite.
Diagnosing mange is sometimes difficult. If mange is suspected, your veterinarian will do a physical examination, including skin scrapings. However, the mites that cause mange are not always found in skin scrapings. If mites are not found, but the signs are highly suggestive of mange, a skin biopsy might be performed.
Sarcoptic mange is highly contagious. Treatment must be thorough and should include all horses and other animals that have been in contact with one another. Your veterinarian will usually prescribe a lime-sulfur solution, to be applied by dip, spray, or sponge. Several treatments, applied 12 to 14 days apart, are often recommended. A group of drugs called macrocyclic lactones are effective against sarcoptic mange. These drugs are usually given by mouth in horses. Treatment for secondary infections may also be necessary.
Psoroptic Mange (Mane Mange)
Psoroptic mange is rare in horses and, in fact, has been eradicated from horses in the United States. It produces lesions on thickly haired regions of the body, such as under the forelock and mane, at the base of the tail, under the chin, between the hindlegs, and in the armpits. The mites can sometimes infect ears and may cause head shaking. The lesions start as small raised areas that soon lose hair and develop into thick crusts that bleed easily. Treatment is the same as for sarcoptic mange (see above).
Chorioptic Mange (Leg Mange)
Leg mange is the most common form of mange in horses and tends to occur in heavy (draft) breeds. Signs start as itching affecting the legs (most often the hind legs) around the foot and fetlock. Raised bumps are seen first, followed by hair loss, crusting, and thickening of the skin. The signs lessen in summer but return with cold weather. The disease persists without treatment, but usually clears when treated. Topical treatments recommended for other types of mange are usually effective.
Demodectic mange is rare in horses. The mites live in the hair follicles and oil glands or in the eyelids and muzzle. The signs of demodectic mange in horses can include patchy hair loss and scaling or skin lumps. Signs appear on the face, neck, shoulders, and forelimbs. There is no itching, so secondary infections do not occur. Treatment is not often done, and lesions can resolve without treatment. This condition may develop in horses with compromised immune systems due to an underlying disease or longterm treatment with corticosteroids.
Harvest Mites (Chiggers, Trombiculids)
Harvest mites usually live on other animals but can infest the skin of horses, especially during the late summer and fall. Signs consist of severely itchy bumps and hives. Specific treatment is not required. The itching can be controlled with medication. Repellents may help prevent infestation.
Straw Itch Mites (Forage Mites)
Straw itch mites usually feed on organic material in straw and grain but can infest the skin of horses. Raised bumps and hives appear on the face and neck if horses are fed from a hay rack, and on the muzzle and legs if fed from the ground. Itching is variable and can be controlled with medication.