I have a mini horse that I believe is allergic to black gnats. There is no grass in his turn out area so it can't be weeds. He eats the same hay as he would if he was in the barn so it's not that either. The only thing that is different from his stall in the barn and the turn out area are the gnats. They are everywhere! We have tried almost everything to get rid of them and nothing is working! My horse has had a golf ball shaped bump under his chin for 2 days now and just last night his bottom lip started swelling up a little bit. I gave him 4 benadryl last night, but it isn't going to permanently solve the problem. I spray him with Bronco spray for black gnats everyday and put a fly mask on him to protect his eyes. I can't leave him in the barn all summer and I'm running out of ideas. Short of putting him in a bubble I don't know what to do. Has anyone used immunotherapy on their horses? How much did it cost? Was it worth it? Any help is appretiated!