Allergies are a common problem in horses which can affect overall health, performance, and quality of life.
Common signs include excessive itchiness, hives, coughing, difficulty breathing (heaves), skin lesions along the lower midline (sweet itch), and hair loss from rubbing. Horses may also have swelling (edema) on the body or legs, swollen lymph nodes, and irritated eyes.
There are many possible causes of allergies. Anything in the environment that the horse ingests, breaths in, or touches can be a possible allergen. Sometimes there is a single incident that causes a reaction such as a bee sting or exposure to a grooming product that sets off the immune system. Often times the allergic reaction is caused by ongoing exposure to something in the environment such as hay, insects, or bedding. Allergies occur seasonally, especially in the spring and summer months as insect exposure increases as do other possible allergens such as plants and pollens. Some horses struggle with allergies year round.
Diagnosis of allergies is based mainly on physical symptoms. Sometimes it is important to rule out other health issues that could lead to similar signs such as infection which could also cause respiratory problems, swellings, etc. Your veterinarian can often do this with a thorough physical exam and possibly a routine blood panel.
When any horse suffers from allergies, the main goal is always to identify and remove the cause if possible.
There may be a new load of shavings right before a horse developed hives. Maybe the hay has been stored for a long time and there is mold or dust at the end of the batch and a horse has developed a harsh cough. There could have been a few unusually warm days in early spring leading to increased insect exposure causing sweet itch. Any strong leads should be investigated and addressed in an effort to remove the cause. Even if the cause seems fairly obvious and easy to remove, the horse may need treatment to get the symptoms under control. Antihistamines are commonly used, fairly effective, and safe for any horse. Some horses benefit from steroids if allergic symptoms are fairly severe. Steroids need to be used with caution, mainly due to the risk for laminitis, and are not safe for horses with metabolic disease. There are topical ointments and sprays that can be used to reduce focal areas of irritation if the horse is wanting to rub or itch excessively. There are a variety of supplements on the market for horses that tend to get allergies. Some are for allergies in general, some for specific forms of allergies such as bug bite sensitivity. I have seen mixed results with many of these products but they can definitely be worth a try in my opinion, especially if they can help manage a chronic case.
In some instances the cause of an allergic reaction is not easy to identify.
In these cases I typically treat the horse with medications to alleviate symptoms for about 1-3 weeks. When the horse is taken off the medications, sometimes the problem will not recur. If the allergies do come back and if the symptoms affect the horse significantly further effort can be made to either modify the environment or run tests on the horse. Modifying the environment can include changes in feed, changing or eliminating bedding, and paying attention to any daily products used topically that could be changed. Even if something is not new to the horse, the horse could develop an allergy, so anything is fair game. It is also possible that the allergen is innate to the environment and can’t be removed. Another option is to submit blood for an allergy panel. The upside to this is that it is relatively easy and noninvasive, maybe less cumbersome than altering environment. The downside is cost and that the results are not proven to be accurate in horses. That said, I have had cases where practical information from blood results helped manage horses. Skin testing is also available for horses for a more accurate assessment of allergens. That is typically done by a specialist in veterinary dermatology and we typically send only the most difficult cases. Once a horse has been tested via skin or blood, allergy shots become an option. This is when a series of shots is given over time to desensitize the horse to allergens that are shown to be significant on their tests. This can be useful, especially if the allergens are unavoidable.
Most horses that experience allergies can be helped with basic management and/or fairly benign medications, especially if caught and dealt with early before the immune reaction gets too out of hand. Luckily, in many cases the issues is transient. If chronic allergies develop it is helpful to understand the pros and cons of the various approaches to treatment.