Horses develop a number of conditions attributed to allergies, but two of the more common are pruritus (itching), which may manifest as rubbing or biting, and recurrent hives. Although biting insects account for many of these allergies, they can also be caused by sensitivities to environmental allergens such as grass, trees, weeds and mites. Environmental allergens should be considered when clinical signs are seasonal and persistent, despite elimination of common causes (e.g., biting flies). If an environmental allergy is suspected, allergy testing can be a helpful tool to identify the cause. Allergy testing can be performed via two different methods.…