Like humans, horses can be allergic to pollens, spores, and other allergens that appear in the environment seasonally, as well as substances found within the barn such as dust, mites, and animal dander. While people tend to respond to these various allergens by sneezing and developing watery eyes, while horses react by getting very itchy skin or developing hives. This leads to constant scratching and chewing which can cause trauma to the skin and extreme discomfort. Generally, symptoms worsen with age and can be controlled, but not eliminated.
Signs & Symptoms
Common symptoms include an often and intense itching, which results in the animal's constant scratching and biting of the irritated skin. Areas most affected in a horse are the face, ears, chest, abdomen and legs. A horse may respond to these symptoms by biting themselves, rubbing against their stall or fence, stomping of their feet, or flicking their tail. An affected horse will usually respond well to glucocorticoids. Secondary skin abnormalities will result from the trauma caused by scratching the itch. These include redness, hair loss, crusts and scaling, ear problems, and skin infections.
Causes & Transmission
Allergens may be absorbed through the skin, inhaled, or ingested. The most common allergens include mites, dusts, danders, molds, weeds, grasses and trees. In addition, some horses are allergic to the dander from other animals in the same dwelling.
Affected AnimalsHorses, humans, dogs and cats. In horses, thoroughbreds and Arabians may be predisposed.
Complications & Prognosis
Inhalant allergy is a life-long disease that tends to worsen with age. Therefore, treatment is required for the duration of the animal's life.
Treatment involves the avoidance of identified allergens when possible, parasite control, and treatment of secondary infections. Essential fatty acid supplements, given at higher doses, can help control the symptoms. Medications can include antihistamines, glucocorticoids, and immunotherapy, or allergy shots. Owners should be aware that long-term use of glucocorticoids may result in complications including iatrogenic Cushing's disease, or excessive levels of glucocorticoids in the body, diabetes mellitus, and worsening bacterial or fungal skin infections. Allergy shots are formulated specifically for individual horses and are administered by an injection under the skin. Improvement of symptoms can take three to twelve months. In addition, shampoos and topical products may be beneficial.
Prevention includes avoiding known allergens as much as possible, and to minimizing complicating factors such as mites, a dirty hair coat, and skin or ear infections. Because the predisposition to inhalant allergies may be genetically transmitted, affected animals should ideally not be bred.
The veterinarian will ask the owner about the horse's history of symptoms. During the physical examination, the presence of itching and skin lesions will be assessed. Before concluding a diagnosis of inhalant allergy, the veterinarian will need to rule out other skin diseases including food hypersensitivity, insect hypersensitivity, mites, and mange. Diagnostic procedures can include bloodwork, skin scrapings, and fungal cultures. Intradermal skin testing is believed to be the most accurate of the allergy tests; this procedure should be performed by an experienced veterinarian or by a veterinary dermatologist.