Reliability of Allergy Tests in Asthmatic Horses

As the most common noninfectious respiratory disease of adult horses, asthma sidelines many horses. Inhalation of organic and inorganic particles triggers the disease in those predisposed to airway inflammation and obstruction. In an effort to relieve horses of the discomfort associated with the disease, including labored breathing and exercise intolerance, horse owners turn to serological tests to pinpoint specific allergens, even if veterinarians disagree on the diagnostic value of the tests.

To determine the reliability of four commercially available tests, researchers enrolled 15 horses into a study.^* Nine of the horses had a history of asthma; the remaining six did not and served as controls. Researchers classified the severity of each horse’s disease using a clinical scoring system, which evaluated several variables, including respiration rate, degree of labored breathing, nasal discharge, frequency of coughing, and multiple measures of lung sound and pressure. Bronchoalveolar lavage and cytology was also performed.

The four allergy tests used in the study included functional in vitro test, intradermal test, Fc-epsilon receptor test, and ELISA for allergen-specified IgE.

“None of the four allergy tests could differentiate reliably between healthy and asthma-affected horses, and no agreement among the results of the four allergy tests was observed,” the researchers concluded. “These tests are probably not suited for an etiological diagnosis of equine asthma.”

If horses with asthma must be stalled, asthma management starts in the stable by reducing exposure to airborne dust, particularly in bedding and hay. Straw seems to have far more respirable particles than other types of low-dust bedding options, such as wood shavings or chopped-up cardboard, so choose bedding for affected horses carefully. Even more important, dry hay brings a large amount of dust into a horse’s environment. Submerging hay in water or steaming hay can reduce exposure to dust by more than half. Hay should be fed from the ground, not from haynets, as hay fed from haynets results in a greater exposure to respirable dust.

Further, any sweeping or blowing of stall floors, aisles, or ceilings should be done when asthmatic horses are out of the barn, well away from clouds of dust. Thought should be given to hay storage, with overhead stacking unadvised.

Medicinal management of asthma should be guided by a veterinarian well versed in respiratory disease, as different medications are appropriate for different situations.

Supplementing with EO-3, a source of the long-chain omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), is one way to moderate the inflammatory response associated with the disease.

“In a consensus statement published by the American College of Veterinary Medicine, the use of omega-3 polyunsaturated fatty acids was listed as systemic therapy for asthma,” explained Peter Huntington, B.V.Sc., M.A.C.V.Sc., director of nutrition at Kentucky Equine Research.^○

“This recommendation was made in part because of a study conducted at Purdue University College of Veterinary Medicine. In that study, horses given long-chain omega-3 fatty acids, particularly DHA, and a low-dust diet had a much more rapid improvement in clinical signs than when fed a low-dust diet alone.”⁺

^*Klier, J., D. Lindner, S. Reese, R.S. Mueller, and H. Gehlen. 2021. Comparison of four different allergy tests in equine asthma affected horses and allergen inhalation provocation test. Journal of Equine Veterinary Science. In press.

^○Couëtil, L.L., J.M. Cardwell, V. Gerber, J.-P. Lavoie, R. Léguillette, and E.A. Richard. 2016. Inflammatory airway disease of horses: Revised consensus statement. Journal of Veterinary Internal Medicine 30:503-515.

⁺Nogradi, N., L.L. Couetil, J. Messick, M.A. Stochleski, and J.R. Burgess. 2015. Omega-3 fatty acid supplementation provides an additional benefit to a low-dust diet in the management of horses with chronic lower airway inflammatory disease. Journal of Veterinary Internal Medicine 29:299-306.