Why & When to test for Equine Allergies (Blog)

In the first of this series of three blogs on equine summer allergies, we looked at how to recognise the common symptoms of allergy and how it is diagnosed by ruling out other common conditions with similar signs. If you missed that blog or want a quick recap the first blog can be found here. In this second instalment we move on to discuss what can be done to investigate the route of the problem once the diagnosis has been made.

 

WHY TEST?

As the expression goes, knowledge is power. Knowing what your horse is allergic to is the first step towards helping, so that you are able to look after your horse in a way that is specific to their individual needs. It allows you to implement tailored strategies to help reduce contact with the problem allergens and access further options for treatment.

The other thing to consider is that equine allergies frequently occur in combination. In research published by Avacta Animal Health last year, we found that horses being allergy tested are unlikely to be positive to just one allergen. In fact, the average number of positive allergens was between 4 and 5 and of the horses that were positive to midges, only 7% did not have positive results to other allergens in addition.*

 

WHAT IS ALLERGY TESTING?

Strictly speaking, allergy testing would be better called allergen identification testing because as already mentioned, it does not diagnose allergy; the diagnosis should be made first by ruling out other conditions. The flowchart below outlines what is involved in more detail:

 

WHEN TO TEST?

As the antibodies we are testing for are produced in response to your horse coming in contact with a particular allergen, for example a grass pollen, once the allergen has gone the number of antibodies found in the blood can reduce quite quickly. This means if tested out of season, for example testing for a grass pollen in the winter, we may not detect the antibodies. For this reason, it’s important to test when the horse’s symptoms are at their worst. This graphic above shows which allergens are prevalent in which season.

Your horse’s management and lifestyle can also significantly affect their exposure to allergens so this must also be factored in. Many horses are stabled for part of the year which will significantly change to which allergens they are exposed.

The different types of indoor and outdoor environmental allergens which horses are exposed to:

 

     

 

Certain medications can also affect the test results and so your vet may ask you to stop them for a certain period of time before testing. This is because to control the symptoms your horse is experiencing, the medication reduces your horse’s immune response to the allergen, which can result in less of the antibodies we are testing for being producing.

Next week, in the final part of this series of blogs, we will discuss the various options available to help with the management of horses with allergies, including many practical hints and tips.

*Forsyth, J., Halliwell, R.E. & Harrand, R. (2019). Co-reactivity between related and unrelated environmental allergens in equine allergen-specific IgE serology testing in the UK. Vet. Dermatol.; DOI: 10.1111/vde.12786