Mites, small, tick-like parasites, cause the skin condition in horses called mange by burrowing into the skin to mate and leave their eggs, says Dr. Rick Parker in "Equine Science." The entire life cycle of the mite occurs on the horse, with eggs hatching after four days and becoming mature adults about two weeks later. These adults mate, lay their eggs, eat dead skin cells and defecate. This causes the itching seen in most mange cases. The cycle continues with various symptoms, until the horse has medical treatment and the mites die.
Sarcoptic mange, although rare in the United States, produces lesions on the neck, head and shoulders of horses, according to the Merck Veterinary Manual. Caused by the Sarcoptes scabiei var equi mite, the lesions start as small, circular, elevated areas of the skin called papules. These develop into vesicles, or blister-like sores. As the horse rubs and scratches at these pruritic (intensely itching) lesions, they become enlarged and crusty, leading to extreme hair loss. If the disease goes untreated, the mange can spread over the horse's entire body, with the skin becoming hardened and folding in on itself, and the animal suffering with anorexia, emaciation and weakness.
Psoroptic mange mites "like to inhabit the mane, forelock, base of the tail or long feathers on the legs of draft-type horse," says Dr. Nancy S. Loving in her article "Hair Loss in Horses." It also produces lesions under the chin and between the front and back legs of these heavily-haired animals, and leads to some cases of severe ear infection and head shaking. Horses typically rub and scratch at these itching papules, causing them to develop into thick, bloody crusts with extensive hair loss in the area of the lesions.
Chorioptic mange, also called "leg mange," affects mainly the heavy, draft breeds of horses with long leg feathers around their hooves, such as the Percheron or Clydesdale breeds. The mites burrow into the skin around the foot and fetlock (ankle) of the horse causing infection, intense itching and papules. As these lesions grow, the skin thickens, becomes crusty and the horse loses its hair on the infected areas. Symptoms of chorioptic mange increase in cold weather, with horses causing damage to sensitive ligaments and tendons by stamping their feet to relieve the itching, says PracticalHorsekeeping.com.
The non-itching Demodex equi mite lives in the hair follicles and oil glands on the skin of horses. Demodex "may occasionally cause small papules or nodules filled with cheesy material" on the shoulders, neck, face and front legs of affected horse, says Dr. N. Bruce Haynes in "Keeping Livestock Healthy." He reports that demodectic mange is self-limiting---heals on its own. Vets typically do not recommend treatment because medications used to treat other species can cause colic and death in horses.
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