My Aunt used to feed her Great Pyr - Iams Lamb & Rice, because the vet told her it was for animals that were allergic to poultry products. The dog loved it until about a year ago, when Iams changed their formula and the vet told her to avoid Iams. He then advised Purina's new "One" and the dog never leaves the bowl till it's empty!
I saw something the other day about phenobarbitol being in pet foods. That's usually reserved for seizures.