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- June 2nd, 2020 - Ask the Vet

By Daniel H. Grove, DVM

First off, I hope everyone is doing well during the COVID-19 times. It is very tough for some out there with lack of work and/or sickness, so take care of yourselves and your horses. We are smack dab in the middle of spring and some people know all about what this month’s article is about. Allergies. Horses are no different than you or I when it comes to allergies. Let us discuss what an allergic response is, how it is manifested and some possible treatments.

An allergic response is a hypersensitivity to an allergen (likely a protein) by the body. The body thinks the allergen is a harmful thing and will mount an immune response against it. When I went to school, allergic responses were categorized into four different types based upon the length of time from exposure to clinical signs and the signs seen. When the body recognizes an antigen (specifically called an allergen in an allergic response) it mounts an immune response against it. The whole process is rather technical, but in the cascade of events, usually histamine is released, and this binds to histamine receptors to cause many of the symptoms we see. As we look to treatments to stop the response, remember histamine is released.

What are the clinical signs? These are different for different allergies, but are commonly associated with where the allergen is encountered. For example, if the horse inhales an allergen, you are likely to see respiratory signs such as cough, and clear nasal discharge, possibly with increased respiratory rate or even difficulty breathing. If the area of contact is the skin, you are likely to see hives, swelling, and pruritis (itchiness). These hives can even have a small area in the center that ruptures, and these can be prone to secondary infections. There are many different signs of an allergic reaction, such as diarrhea, but respiratory and skin manifestations are the most common.

Treatment of an allergy is going to be based on a few things such as duration, possible cause, severity of reaction, and the horse’s underlying medical history. For a mild case of a few hives, we may choose benign neglect, or just let it run its course. For chronic seasonal allergies, we might choose an antihistamine that is good for long term use. It acts by binding to the histamine receptors without activating them and competing against histamine. For a severely swollen muzzle that might block airflow, we are likely to incorporate corticosteroids like dexamethasone in our treatment. These drugs work by reducing inflammation and the immune response itself, but they have the potential to have some side effects, so it is important for your veterinarian to know your horse’s history prior to using them.

Allergies are annoying most of the time. Sometimes they are life-threatening. Make sure you discuss with your veterinarian the symptoms your horse is displaying and come up with a treatment plan with them so you can keep your horse feeling well and ready for your ride.


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