Hello Megan! The first step is to identify the allergy's source. To achieve this, you need to call your veterinary. He will inject minuscule amonts of allergen in the skin and monitor the reactions over a 24 hour period. Blood testing is much more prevalent and involves testing the blood with different allergens to see which ones cause a reaction. Sometimes an allergy test will be conducted and the horses will show sensitivities to everything.
Careful management is the best weapon against skin allergies, attempting to minimize the horses’ reactions by protecting him from exposure to the things that set off his allergies. For a horse that is affected by flies and biting insects, the use of fly repellents, keeping him indoors during the worst times for insect bites, or using a light sheet to protect his body can be helpful. But if a horse continually develops hives or other symptoms in spite of all your precautions, you may have to treat the horse with steroids every second or third day to help clear up the allergy and alleviate the discomfort. Daily dosing with steroids is not recommended, since this may have harmful side effects over time, such as damaging the adrenal glands or compromising the immune system.