For the one-time occurrence of hives, you might never discover the incriminating source. However, if hives recur, you might be motivated to track the allergen. Start by mentally reconstructing any changes in diet, environment, medications, vaccinations, or stress factors that occurred in recent months. Provide your veterinarian with a list of suspicious items. Time-honored strategies for managing hives eliminate ingestion, contact, or inhalation of as many things as possible. With a little sleuthing, you might be able to identify the cause and successfully eliminate the problem from your horse’s future.

Another diagnostic technique, albeit expensive and time-consuming, uses intradermal allergy testing to try and isolate an allergic source from pollens (plants, bushes, and trees), molds, grasses, weeds, dust mites, insects, and farm plants. The horse should be pulled off medications (steroids or antihistamines) at least 10-30 days prior to testing.

Once a particular antigen has been identified, immunotherapy (historically referred to as hyposensitization) injections might target that allergen. The process is slow and should be continued for at least a year. Hensel describes the process: “By injecting small amounts of allergy vaccine, a horse’s immune system should become tolerant to the allergen over time, resulting in mild to no reaction during re-exposure