My 8 y/o female GSD is having allergy problems. Her skin is black around her belly and she has bumps or sores on the blackened area that she's always licking. I had her to the vet and he said it was an allergic reaction. He prescribed Prednisolone which seemed to help for a while. Then he knocked the dose down and the flare up came back. I was wondering if it's something in her diet causing the reaction. My neighbor's shi-tsu has to eat a certain brand of dog food or she gets allergies as well. I'd like to try a different food and see if that's the problem. Any recommendations?