Researchers at Ghent in the Netherlands undertook a literature search (PubMed) to determine what was known regarding food allergies in the horse from an evidence-based point of view. They searched using the terms “food allergy”, “food intolerance”, ‘adverse food reaction” and “horse/equine”. They defined a food allergy as “an adverse immune response to specific food components, typically proteins.” Diagnosis was based on the clinical history and supported by testing (skin testing, blood testing, food trials). They then explored different types of allergic reactions and arrived at two conclusions:
Horses naturally develop type I hypersensitivities (immediate-type allergic response, IgE driven)
To date, only an IgE mediated (driven by IgE) allergic etiology has been confirmed for skin hypersensitivity associated with Culicoides midges in horses (“Sweet Itch”)
They went on to suggest that pruritus (itchiness) is a common complaint with equine skin disease, and food allergies may contribute to this. In conclusion, this research group found that the presence of food allergies remains to be substantiated in horses. Food allergy diagnosis should be based on the clinical history and supported by a food elimination trial, with a recurrence of symptoms when the suspect food is reintroduced. Diagnosis by blood testing remains the best alternative (as skin testing is somewhat unreliable in the horse), but the validation of an allergen-specific IgE blood test has not yet been done for the horse (at the time of this article).
Allergies in the horse remain a frustrating condition for both owner and veterinarian. Within the Friesian breed, some of our horses are affected with hypersensitivity to Culicoides that can be difficult to manage, as well as some of the skin issues that are seen secondarily to Chronic Progressive Lymphedema. The more we learn about allergies, the better we will be able to help our affected horses stay comfortable through management and medication if or when needed.
Scientific Article: van der Kolk, JH, et. al. Food Allergy in horses: what do we know? Proceedings of the European Equine Health and Nutrition Conference, 6th ed. , March 2013.