Managing Allergies in Horses

Horses can develop hives in response to medications, insect bites, or allergies to feed or the environment. Hives usually resolves on its own or with a short course of medication. In some cases, however, the rash, intense itchiness, and trauma to a horse’s delicate skin secondary to scratching and rubbing can persist, posing both diagnostic and treatment challenges for veterinarians and owners.

“A long-term sensitivity to environmental allergens or feed resulting in pruritus is referred to as atopic dermatitis,” described Laura Petroski-Rose, B.V.M.S., a veterinarian for Kentucky Equine Research.

Common causes of atopic dermatitis may look familiar, as many also contribute to equine asthma, such as dust, storage mites, insects (e.g., Culicoides), pollens, and feed ingredients.

“Not only is diagnosing atopic dermatitis challenging, managing affected horses also proves frustrating at times,” relayed Petroski-Rose.

Recommended treatment strategies include allergen avoidance, topical therapies, and systemic medications such as antihistamines, glucocorticoids, and tricyclic antidepressants.

“In addition, owners can help support the health of their horse’s coat and skin with Bio-Bloom PS, a supplement containing biotin, iodine, chelated zinc, and methionine, all of which play a role in maintaining healthy skin, hair, and hooves,” explained Petroski-Rose.

She added, “Products that contain omega-3 fatty acids, such as EO-3, are also excellent for skin and coat conditions as they possess natural anti-inflammatory properties.”Australian owners should look for Bio-Bloom as well as EO-3.

Due to a dearth of data, the relative success or failure of these treatments or general management strategies for horses with chronic atopic dermatitis remains unknown. In a recent study*, 58 owners of horses that had intradermal skin tests were interviewed. The veterinary researchers unearthed some very interesting facts.

“Four of the 58 horses were euthanized due to uncontrollable skin disease but, on the flip side, 18 horses had not shown evidence of skin disease for at least two years,” relayed Petroski-Rose.

The researchers also reported that 29 horses still required medication to control skin disease. Of those, owners reported a beneficial effect of the following:

• “Allergy injections” (referred to as allergen specific immunotherapy, or ASIT, based on allergy testing results) in 9 of 14 horses;

• Glucocorticoids in 33 of 35 treated horses;

• Antihistamines in 17 of 28 treated horses; and

• Management changes implemented for allergy avoidance in 9 of 22 horses.

Clearly, no single treatment strategy exists for horses suffering from chronic skin issues due to suspected allergies. As with many chronic conditions affecting horses, a multimodal approach, including nutritional supplementation, likely works best.

*Loeffler, A., D. Herrick, S. Allen, and J.D. Littlewood. 2018. Long-term management of horses with atopic dermatitis in southeastern England: A retrospective questionnaire study of owners’ perceptions. Veterinary Dermatology 29(6)526-e176.