Often, I am asked about feeding horses with allergies, which tends to confuse me because there are very few documented cases of true food allergies. In fact, most allergens for horses are environmental – mold, pollens, mites and other insects, etc. – that may or may not be associated with a feed ingredient, but not the feed itself.
I have also heard from many horse owners that they have had allergy testing done on their horses, and while I knew many of these allergy tests were not fully reliable in other species, it was only after seeing a recent article by Dupont and coworkers, that I learned serum testing is not a viable screening tool for food allergies. The paper titled: “A commercially available IgE-based test for food allergy gives inconsistent results in healthy ponies,” by Dupond, De Spiegeller, Liu, Lefère, van Doorn and Hesta was published recently in the Equine Veterinary Journal (Oct. 7, 2014; doi: 10.1111/evj.12369).
The test screened healthy ponies for serum IgE, which is associated with the more common type 1 hypersensitivity, IgE mediated type of allergy, that is associated with hives, itching, runny eyes or head-shaking. Detailed analysis of the serum samples were run against typical feeds, such as soy, corn, wheat, alfalfa and rye. Six of 17 ponies tested positive upon initial screening and were then tested against each allergenic feed to provoke an allergic response and were monitored for changes in heart rate, respiratory rate, temperature and fecal consistency, along with screening for hives, itching and colic symptoms and additional bloodwork.
The results found that despite having positive IgE screening tests from a commercial laboratory, the ponies did not show an allergic response to the foods themselves, when tested with the gold standard method for food allergy diagnosis; the provocation test.
The study would have been stronger had known allergy cases been included in the group tested, but these were no such horses available.
The authors concluded that the IgE based food allergy test was inconsistent, and inaccurate results may lead to unnecessary restrictions in feed selection for these horses.
Interestingly, intradermal skin testing for environmental compounds and insects also have some misleading results, though no research has been conducted with this type of testing on feed allergens.
Therefore, the best practice for a suspected feed allergy or sensitivity is the elimination and provocation test – to remove the suspected feed to see if symptoms clear and reintroduce the feed to confirm.