Horses, like humans, do suffer from a wide variety of allergies. From tree to grass pollen, to everyday dust and mold, to insect bites, and even certain foods, a certain subset of horses will experience some level of allergic reactions. However, identifying what exactly a horse is allergic to can be a long and expensive process. Thus, when it comes to allergy testing, owners need to be aware of how proper allergy testing is done and why it can be unreliable.
What Types of Allergy Tests are Available to Horses?
Many of the allergy tests used in human health have been adapted to be used in horses. However, some of the more intensive allergy tests can be quite exhaustive and expensive. Yet, even the best methods can still provide false positives or negatives and thus, are not always accurate.
- False positives are when a test indicates an allergy to a specific substance, when in fact the horse does not have an allergic reaction to it.
- False negatives are those when the test indicates no allergic response to a specific substance, when, in fact, the horse is allergic to it.
There are allergy tests being commercially sold that can be considered quite unreliable. Regardless, skin testing is often considered the best and most helpful method of testing for allergies in horses. Yet, this can be expensive and is not always accurate.
- Skin testing involves shaving a portion of the horse, usually around the neck area. Then, potential allergens are injected subcutaneously under the skin in a large pattern.
- The horse is then monitored for 24 hours for any potential reactions. Some allergic reactions are immediate, while others manifest over the 24-hour period.
- A positive response will be a red, raised area of skin, which is called a “wheal.” The larger the wheal, usually the greater degree of sensitivity to the allergen.
Another method of allergy testing that may be used by some practitioners is blood testing.
- Blood draw from a horse is used to measure the levels of immunoglobulin E (IgE) antibody.
- In a total IgE test, high levels of IgE in the blood may indicate the horse is having an allergic reaction to an undefined allergen or allergens.
- In a specific IgE test, a horse’s blood is used to test IgE reactions to a panel of suspected allergens, like pollen, mold, insects, and even certain foods. Generally, if IgE levels spike in response to an allergen, it may indicate the horse is allergic to that substance.
Another test being sold commercially to horse owners is hair testing for allergies.
- Relies on testing of the hair shaft. Thus, most owners use the mane for testing.
- Depending on the commercial kit used, most will look for a reactivity test like that described in the specific IgE test. Hair is used to either react with IgG or a method to detect allergies called “bioresonance.”
How Can Allergy Testing be Inaccurate in Horses?
As mentioned, skin testing can be the most helpful or reliable method for testing for allergies in horses. However, it is not always accurate with some false positives and false negatives.
- A positive skin response to a substance injected under the skin does not necessarily mean the horse is having difficulty or a whole-body reaction to that substance. Meaning, a positive skin response to say tree pollen, does not always mean the horse is having any problems or with tree pollen in its environment.
- If during the testing process, if the dose given is too large, any horse may display an allergic reaction.
- Alternatively, a horse may not react at all to the injected allergen even if they are truly allergic to that substance (false negative).
Blood testing for allergies in horses is proving to be unreliable.
- IgE allergy testing have a history of high levels of false positives and false negatives.
- High levels of IgE circulating in the horse may be normal and not always indicative of an allergic response.
- In specific IgE testing, elevated IgE levels to specific substance does not always corelate to clinical symptoms in the horse.
- A study published in 2016 out of Europe reported inconsistent results in IgE testing of horses for food allergies. This is similar to reports in other species like humans.
The testing of hair for allergies is the most problematic and least reliable method for horses.
- There is a lack of scientific evidence in any species, to include horses, to demonstrate hair testing as a reliable method of testing for allergies.
- The reliance of using the hair shaft means that trace amounts of the allergens can be present in the hair (i.e., pollen), which can influence test results.
- Has shown to have a very high rate of false positives and false negatives.
- Has been rejected by the medical community as an unreliable and described as not effective for testing horses (or humans) for allergies.
- Bioresonance for allergy testing in horses, or in any species, has no scientific backing. There is currently no evidence to support bioresonance on diagnosing or treating any medical condition.
What Are the Best Methods for Identifying Allergies in Horses?
Despite its ability to give some false positives and false negatives, skin testing continues to be the best method on trying to identify allergens. The practicing veterinarian can then use the horse’s clinical history, region it lives in, abundance of allergens in the environment and other factors into identifying potential allergies to specific substances.
For food-specific allergies, the best method is to conduct an elimination trial. The suspected feed ingredient should be removed from the diet with observations of the horse. If symptoms subside, the feed ingredient should be reintroduced. If the horse has an allergic reaction, then they appear to be allergic to that feed ingredient. More can be read in our Food Allergies in Horses article.
Where allergy testing may be useful for horse owners is for the possibility of allergen-specific immunotherapy (allergy shots). Here, horses are challenged with increasingly levels of the specific allergen and the horse’s immune system will develop immunity to the allergen over time. Most horses can improve within 6 months to a year after starting treatment.
Take Home Message
Allergy testing like skin tests can be helpful to a veterinarian when diagnosing horse allergies. The other types of allergy tests like IgE blood tests and/or hair tests have shown not be reliable methods of testing for allergies in horses. When it comes to food allergies, the best method to determine if a horse is allergic or not is through a feed elimination trial. If you need any guidance in what you are feeding your horse, you can contact us for a free consultation.
References
Dupont, S. et al. (2016). A commercially available immunoglobulin E-based test for food allergy gives inconsistent results in healthy ponies. Equine Vet Journal 48:109-13.
Morgan E. E. et al. (2007). A comparison of intradermal testing and detection of allergen-specific immunoglobulin E in serum by enzyme-linked immunosorbent assay in horses affected with skin hypersensitivity. Vet Immunol. Immunopathol. 15:160-7.
Tahon, L. et al. (2009). In vitro allergy tests compared to intradermal testing in horses with recurrent airway obstruction. Vet. Immunol. Immunopathol. 15:85-93.
Wong A.W. et al. (2022). Issues surrounding consumer-bought food allergy testing. Clin. Exp. Dermatol. 47:547-552.
