Feeding Horses with Suspected Allergies

It can be difficult to pinpoint the true case of a horse’s allergic symptoms. Environmental allergies are significantly more common than food allergies, which can only truly be diagnosed through an elimination diet. If the offending ingredient can be identified, enlist the help of a nutritionist to recommend an appropriate commercial product or to formulate a custom diet.

Eliminate other causes

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 aspects of the diet because that is often what they have most control over. However, environmental factors- such as mold or pollen or a skin hypersensitivity to in­sects or plants are the most frequent culprits. Hives, runny eyes, nasal discharge and coughing are 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.

To help minimize exposure to respirable dust and molds:

• Trade long-stemmed hay for a complete feed
• Wet hay thoroughly before feeding
• Feed at ground level
• Wet stall bedding or change the type of bedding
• Provide as much turnout time as possible

To help manage horses with skin irritations:

• Change or eliminate topical products
• Use fly sheets and adjust pasture turnout to help reduce exposure to insect bites
• Use appropriate medications during the horse’s “difficult season”
• Supplement with a source of omega-3 fatty acids, such as Purina^® Amplify^® High-Fat Supplement

A Note on Diagnostics

Serum allergy testing is a convenient 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.^1,2 Intradermal skin testing is the gold standard for diagnosis of skin hypersensitivities but has limitations in the field. Position statements made by the American College of Veterinary Dermatology state unequivocally, that neither serum allergy testing nor intradermal skin testing are valid tests for the diagnosis of food allergies and the identification of specific food allergens. The only test that can accurately diagnose food allergy is an elimination diet.

Conducting an Elimination Diet

If symptoms are otherwise unexplained, it is time to closely evaluate the diet.  When only one or two feed ingredients are suspected, contact the feed manufac­turer for a product recommendation that does not contain the suspect ingredients. Certain feeds, Omolene^® 400 is one example, are formulated intentionally without some common allergens such as alfalfa and oats. However, when there is a long list of potential allergens it becomes extremely difficult to find a balanced feed free of all the suspect ingredients. In these cases, a true elimination diet is required.
 
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, then ingredients can be reintroduced one at a time until clinical signs reappear, thereby identi­fying the allergenic feed ingredient to avoid.

Designing the diet

In cases with confirmed sensitivities where there are mul­tiple offending ingredients or ingredients that are particu­larly hard to avoid in commercial feeds, it may be neces­sary to enlist the help of an equine nutritionist  to design a balanced diet. Diets that provide necessary nutrients to maintain body condition and fuel for the performance horse might include alfalfa hay, a vitamin/mineral supplement such as Free Balance^® 12:12 Mineral, grain (oats/barley/corn) for energy, oil for added calories, some beet pulp to hold it together and, if a soy-free source of quality amino acids is required, Mare’s Match^® milk replacer can be used. Clearly this can become cumber­some for the horse owner to maintain, hence the due diligence to make sure it is truly necessary.
 

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¹ Dupont, S., A. De Spiegeleer, D. J. X. Liu, L. Lefère, D. A. Van Doorn, Hesta, M. 2014. A commercially available immunoglobulin E-based test for food allergy gives inconsistent results in healthy ponies. Equine Vet. J. DOI: 10.1111/evj.12369
² Bethlehem, S., Bexley, J., Mueller, R.S. 2012. Patch testing and allergen-specific serum IgE and IgG antibodies in the diagnosis of canine adverse food reactions. Vet. Immunol. Immunopathol. 145, 582-589