What they finally settled on was continuing the cephalexin (every other day), using Atopica, and keeping her on the single-protein raw diet + minimal supplements and no carbs. It didn't completely fix the problem, but it gave them another year before they had to euthanize her.
To be honest, I haven't seen a dog with true food allergies -- only environmental allergies and chemical sensitivities that are made worse by certain foods. Dogs don't become immune-compromised because of food allergies; they have issues with food because their immune systems are too weak, either from poor genetics or environmental exposure to toxins (or both). In Copper's case, having likely been the product of casual breeding herself, having produced at least two litters of puppies before she was two, and being exposed to repeated vaccines, flea/tick preventatives, low quality food, and stress -- all added up to produce her immune issues. One of the rescue dogs (who came from a Missouri high-volume breeder) I worked with had the exact same issues, exact same lack of progress from treatment.
I'm sorry that's not the happiest story to tell. I hope that whatever you try for Petey is more successful than what was tried with Copper. As for the food, the only thing you can do is try it.
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