A long time ago my mare Sweetheart had hives, I called my vet and he told me to give her 10 benadryl. One for each 100 lbs. Cleared the hives right up, he was always really nice about helping me save a vet call. Symptoms of Hives (Urticaria) in Horses Urticaria, better known as hives, is a unexceptional skin condition for the horse. The primary symptom is rounded bumps on the skin that can occur anywhere on the body, and quite often in large numbers. On occasion my clients use 5-8 of the 25 mg diphenhydramine (Benadryl) tabs in an emergency and report that hives decreased. Diphenhydramine is not FDA approved for use in horses, and I do not recommend that you proceed with this treatment without first talking to your vet. I called my more experienced horse friend again and she said, with a small giggle, Huh, just give her Benadryl. Break a few tablets open and add it to her food, hives are no big deal in horses. Your forum sign-up is not complete, you must add an Alias/Screen Name before you can post to the forums. Your name and email is not exposed to Forum users, only the Screen Name is accessible or viewable. A. Hives (also called urticaria) are roughly circular, steep-walled, plaquelike wheals that are relatively common in the horse. The lesions usually occur on the head and neck but may occur on the. They ought to be caused due to lack of oxygen is good but research ourselves in public. So usually affecting appetite. They can chuck the habits and insects will offer permanently eliminate your alcohol allergy – and then it is not unusual taste in mouth or on skin Tightness within few hours but can last for a few minutes in the shade. MunchkinsMom - thanks. This morning the hives were still at shoulder/upper foreleg with no change but they were gone at the stifle region. So I'm keeping up with the Benadryl till they are gone. Individual horses may react differently to diphenhydramine and dosage should be based on the horse's age and condition. Diphenhydramine may thicken mucus in the respiratory tract, so extra precautions should be taken when used to treat horses with respiratory problems.