I bought my TB as a 2 year old in November and the following spring she developed hives. She had never had them before according to her former owner. I had 2 vets see her and one gave her antihistamines which did not help at all. the other vet suggested omega 3 fatty acids and she is now on Horseshine. WE could never find a specific cause. The horseshine helped dramatically and I also used medicated shampoos which helped also. I got that at petsmart. A friend had a benadryl shampoo which also worked but its not made any more. I managed to avoid dexamethasone though I used topical steroid cream on the biggest welts. Once the weather cooled off she got better and this year she has only had a few hives. She remains on the Horseshine. I tried everything to find a cause. new brushes. different hay and bedding and different feed but the horseshine made the biggest difference.