Equine Allergies: Immunotherapy and Omega-3s

Insect bite hypersensitivity, atopic dermatitis secondary to food allergies, and recurrent airway obstruction are all examples of the horse’s immune system overreacting to normal stimuli, often involving the antibody known as immunoglobulin E (IgE).

Diagnosing allergies in horses is not clear-cut. Skin allergy testing, for instance, provides inconsistent results, which can be frustrating for owners. Without a clear idea of the suspect allergen, implementing effective therapies is nearly impossible.

“The two available tests are an intradermal test, or IDT, and a blood test. The IDT involves injecting a small volume of liquid allergen, usually pollens, molds, or insects, and noting whether or not swelling, called a wheal-and-flare skin reaction, occurs at the injection site. The blood test measures specific IgE levels produced in response to allergen exposure,” explained Laura Petroski-Rose, B.V.M.S., a Kentucky Equine Research veterinarian.

Neither of these tests has been fully validated, and disparities in their results have been reported, said Petroski-Rose.

Despite this, owners of horses with clinical signs of specific allergies sometimes elect to pursue allergen-specific immunotherapy (ASIT), which involves injecting increasing quantities of an allergen-containing extract. This practice is believed to work by modifying the immune system’s response to future exposure to allergens, potentially by decreasing IgE. Whether or not this technique works in horses remains unclear, according to Petroski-Rose.

In a recent study*, veterinarians used either the IDT or blood test to identify potential allergens in 19 horses presumptively diagnosed with atopic dermatitis. IgE levels were then measured intermittently over the next two years.

“Researchers found that ASIT decreased IgE levels in treated horses, and that significant clinical improvements in skin allergies were noted in 85% of included horses over the 24-month study period,” relayed Petroski-Rose.

She added, “Offering marine-derived omega-3s, such as those found in EO-3, also helps horses with allergies and supports the immune system. Numerous reports suggest that omega-3s DHA and EPA can be an effective nutritional defense to potential skin problems.”

*Radwanski, N.E., D.O. Morris, R.C. Boston, et al. Longitudinal evaluation of immunological responses to allergen-specific immunotherapy in horses with IgE associated dermatological disease: A pilot study. Veterinary Dermatology 30(3):255:e78.