Horse Allergies. Are Your Horse's Allergies, Real? Horse Allergy Testing.

Food Allergies In Horses-How To Determine If Your Horse's Allergies Are Real & How To Treat Them, Medically.
by Amy M Gill, PhD
Equine Nutrition, Lexington KY

Over the past several years, testing horses for horse feed allergies has become very popular in veterinary practice. When a horse develops a skin and/or respiratory problem, the feed or hay the horse is eating immediately becomes suspect as a causative agent. What is most alarming about this trend is that the horse is limited to vegetarian dietary ingredients and the list of possibilities that can be used to make horse feeds are limited to about twenty. It has not been uncommon for the allergy test to come back reporting the horse is allergic to almost all the ingredients in the feed. So, if we take the results of these tests at face value, what exactly can we feed to a horse if he is allegedly allergic to almost everything? Obviously in reality this would be an impossible situation to resolve.

Many normal horses will react to at least some of the allergens on the allergy panel. In other words, normal horses can have positive reactions to allergens that they are actually not allergic to.

To complicate matters, the panel of allergens used on the test may not contain the allergens that the horse is actually allergic to, so testing for what the horse truly needs to stay away from may be overlooked.

Therefore, the history and method of allergy testing needs to be examined in depth so that a clear understanding of why horses appear to be allergic to a high percentage of food ingredients exists.

Many veterinarians that do not specialize in allergies routinely use blood testing methods. There is a great deal of controversy about the reliability of blood testing because the organ that is affected most - the skin- is not being tested for a reaction. Additionally, there are several different types of blood tests offered which may vary in accuracy of results and the lack of standardization between laboratories makes the validity of the test and the final results questionable.

Most Veterinary Dermatologists use a method of allergy testing known as intradermal allergy tests (IDAT). This test involves injection of allergens such as mold and pollen into the horse’s skin, usually in the neck area. The dermatologist then examines the skin for a reaction that is called either wheals or hives. These are measured for several hours and at that time the largest wheals indicate which allergens should be used in hyposensitization injections. It is important to note at this point, that neither blood testing nor intradermal skin testing are very useful for identifying allergy to foods. Food allergy in horses is rare and a real diagnosis can be confounded by allergy tests that often show hypersensitivity to something the horse commonly eats. Clinical signs of food allergy include hives, itchiness, and possible self-trauma due to scratching. The best and most dependable method of testing for food allergy in horses is to forgo all the fancy blood and skin tests and to simply eliminate the suspected food allergen from the diet for 4-8 weeks and to see if the condition improves.

If a specific food allergen cannot be pinpointed, a practical way to begin a food-allergy trial is to remove concentrates (grain or pellets) and all supplements from the horse’s diet and just feed forage. If the condition improves, the concentrate could be fed again to see if the hives or itching returns, or simply try another feed and be happy if the symptoms do not re-appear.

In many cases, stabled horses become highly sensitized to mold, pollen, moisture, ammonia and poor ventilation. Stress from confinement can also cause compromised immune function which can lead to a predisposition for allergies. Getting horses out on pasture and lowering stress levels may do more good than anything for what appears to be an allergic horse.