Q: I have a friend who claims her horse is allergic to oats, as confirmed by a food allergy test. Are food allergy tests in horses accurate?

A:  Serum allergy testing is a convenient testing method that is growing in popularity and, when paired with clinical signs, can be a place to start for non-food allergens. However, it has significant limitations and is prone to false positives for food allergens in horses and other species. Position statements made by the American College of Veterinary Dermatology state that neither serum allergy testing nor intradermal skin testing are valid tests for the diagnosis of food allergies or the identification of specific food allergens. The only test that can accurately diagnose food allergies is an elimination diet.

This is the thought process I follow when faced with a horse that appears to be suffering from allergies, or the owner suspects allergies. First, consider the horse’s clinical signs, which should narrow the field of what is truly affecting the horse. Horse owners are quick to look to the diet because that might be what they have most control over. However, environmental factors such as mold, pollen, or a skin hypersensitivity to insects or plants are the most frequent culprits. Hives, runny eyes, nasal discharge, and coughing might be indicative of an inhaled allergen. Symptoms that have seasonality or that come on suddenly despite a consistent diet are unlikely to be resolved by changing the concentrate portion of the diet.

If symptoms are otherwise unexplained, it is time to closely evaluate the diet through an elimination diet. A horse that’s been on a good plane of nutrition previously can be fed a hay-only diet for at least two to four weeks to observe if the symptoms resolve. If there is no improvement in symptoms, a food allergy is unlikely. If symptoms resolve, ingredients can be reintroduced one at a time until clinical signs reappear, thereby identifying the ingredient to avoid. In the case of the suspected oat allergy or when there is an allergy to only one item, it can be relatively simple to read the ingredient list or contact feed manufacturers to find a formula without that one item. However, when multiple ingredients are suspected, the importance of the elimination diet is even greater. Otherwise, you might unnecessarily limit your feed options or end up with an unbalanced or inefficient diet. As always, consult an equine nutritionist when in doubt.

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