Having a problem with Innova Evo?

I have a Toy Xoloitzcuintli named Scooter. He is 2 years old and he has been eating Pro Plan since he was weaned. His breeder fed Pro Plan and that is what I've continued to feed him all his life. Recently I've jumped on the "natural" band wagon and I've tried what is supposed to be a better quality food. I bought a small bag of Innova Evo Herring & Salmon to try. A half hour after his first meal this morning he has broken out in hives! I'm not sure what to do. I'm pretty sure this is caused by the food. Has anybody else had this problem with Innova Evo? I don't know weather to continue trying to feed it and maybe he will get used to it, try another food, or go back to Pro Plan. I would really appreciate some advice here.