you need to feed a novel protein diet avoiding beef, chicken,lamb,rice, corn and wheat. thats why just switching brands doesn't work, most diets have one of those ingredients. I tell clients we may need to try several.....duck and potato, rabbit based etc. I typically don't use venison or bison because a vet dermatologist i heard at a meeting said they were too close to beef. You might even have to try a hydrolyzed protein diet like Z/D. Feed the diet EXCLUSIVELY for 4-6 weeks (nothing can cross their lips but that diet and water...no treats, rawhides, milk bones etc) and see if it helps. May take several tries. Go to a big pet food store and you will find several brands that may work, be sure to check the small ingredient label on the side of the bag to avoid the antigens mentioned. Your vet can write a script for one as well from Royal Canin, Science Diet etc or even Z/d. I tell my clients you have a 20% of helping allergies with diet but if you had a 20% chance of hitting the power ball lottery you would play every week! Also you don't have a bunch of lab fees and you had to feed the dog anyway. Good luck1