A variety of skin conditions affect the outside part of the ear, called the pinna. Most conditions cause tissue changes elsewhere as well. Rarely, a disease affects the outer ear alone, or it is the first site affected. As with all skin conditions, a diagnosis is based on a thorough history, a complete physical and skin examination, and carefully selected diagnostic tests.
Insects and parasites commonly cause inflammation of the pinna in horses—-resulting in redness, swelling, itching, or blistering—either through direct damage from the bite of the parasite or as a result of hypersensitivity.
Equine aural plaques are benign, raised, pinkish tumors on the inner surface of the ear. They are caused by a papillomavirus that is likely transmitted by black flies. These flies are active at dawn and dusk, when they attack the head, ears, and lower abdomen of horses. The thickened, hard, round bumps and patches eventually grow together. Often both ears are affected. Similar lesions may be present around the anus and external genitalia. The plaques do not usually cause signs, but in some cases the direct effect of the fly bite causes skin inflammation and discomfort. Treatment includes frequent applications of fly repellent and stabling the horse during the hours when black flies are active. The plaques typically do not go away.
Fly strike (irritation of the ears caused by biting flies) is a worldwide problem in horses caused by the stable fly. The fly bite causes small, hard, round bumps and raised, reddened areas with central bloody crusts that itch. Tissue changes are found on the tips of the ears. In horses, the stable fly can cause a hypersensitivity reaction or severe inflammation of the skin resulting in tissue changes on the hind and/or lower part of the body and face in addition to the outer ear. Treatment includes fly repellents, controlling the fly population with environmental cleanup (for example, removing manure), and insecticides.
Frostbite may occur in animals poorly adapted to cold climates and is more likely in wet or windy conditions. It typically affects body regions that are not well insulated, including the tips of the ears. The skin may be pale or red, swollen, and painful. In severe cases, death to tissue and shedding of the pinnae tips may follow. Treatment consists of rapid, gentle warming and supportive care. Amputation of affected regions may be required but is usually delayed until the extent of living tissue is determined.
Several immune-mediated diseases may affect the outer ear and ear canal (see Immune Disorders of Dogs: Autoimmune Skin Disorders). Other areas of the body are typically affected and may include mucous membranes or skin. Immune-mediated diseases are confirmed with a biopsy of primary abnormalities.
Nonburrowing psoroptic mites cause an itchy, inflamed ear canal in horses. Horses may shake their heads and have a drooping ear. Diagnosis is confirmed by finding the mites on skin scrapings or in ear discharges, but mites may be difficult to find in the ear canal. Psoroptic mange is a reportable disease in some regions. Medications are available for controlling these conditions. Your veterinarian will prescribe the one that is most appropriate for your horse.
Ticks can cause irritation at the site of attachment and may be found on the pinna or in the ear canal. The ear tick, found in the southwestern United States, South and Central America, southern Africa, and India, is a soft-shelled tick whose younger, immature forms infest and live on the external ear canal of horses. Signs of infestation include head shaking, head rubbing, or drooped ears. Both the animal and the environment (pasture and stable) should be treated. Your veterinarian can recommend the most appropriate treatment for your horse.
Last full review/revision July 2011 by T. Mark Neer, DVM, DACVIM; Michele R. Rosenbaum, VMD, DACVD; Patricia D. White, DVM, MS, DACVD