Sarah Birkhold B.S, DVM
Just like people, horses get allergies as well. Allergies can manifest in the skin, or lung disease known as equine asthma, or heaves. Environmental allergies are most common and will be the focus of our discussion. So that begs the question, why do horses get allergies and can we cure them?
Depending on the geographical location, your horse will be exposed to a number of different allergens including mites, insects, grasses/hay, trees, weeds, and fungi. Each horse will have varying ability to “defend” itself against specific environmental allergens. During development, if the horse is exposed to specific environmental antigens then the chance of becoming allergic to that allergen later in life is reduced. Genetics play a large role in the horses susceptibility to environmental allergens as well. The development of environmental allergies is based on a combination of early exposure to the antigen in life, and genetic predisposition.
How do I know if my horse has environmental allergies?
Your veterinarian will be able to make a decision regarding allergies to your horse. Since environmental allergies can look similar to skin lesions from autoimmune disease, mites, lice, and other ectoparasites, it is important to have a professional evaluation. Environmental allergies typically present with either specific patterns or generalized dermatitis and hypersensitivity reactions. Some types of environmental allergies, known as sweet itches, will often follow itching patterns along the chest, face, neck, tail head, and lower belly along the midline. Other generalized environmental allergies will present with signs of itching all over the body with small raised, sometimes crusty bumps or non-haired patches. In cases where the horse has had environmental allergies for a long period of time, the skin will become thick and tough referred to as lichenified.
How do you treat allergies?
If the allergies are rather mild, usually a combination of medicated shampoos, environmental modification, and antihistamines can control the allergies during the seasonal flare. In horses that have moderate to severe allergies, purified antigen vaccines are a better option.
Will medications cure my horses’ allergies?
No. Just like humans, our goal is to reduce the immune response to environmental allergens. Therefore, long-term control is achieved with long-term care. Purified antigen vaccines, known as allergy vaccines, are a great option to reduce the immune response to an allergen. This can be obtained with either serum allergy testing or an intradermal skin sensitivity testing. The allergens tested are specific to the horses’ geographical area. Your horse will have a better control of clinical symptoms the earlier in life the purified antigen vaccines are started. It is much more difficult to achieve resolution of clinical signs in an older patient with long term environmental allergies.