I agree w/ Nicole - Tylan can work very well for some dogs.
And btw, Elliemay told me that the "Starch" in the HA food is Corn Starch - so that could also be irritating. When telling me about that, she also mentioned Metronidazole (can work for some) and Prednisone. Which begs the question, why didn't the vet put him on Pred. after doing a biopsy?
You might also consider a 2nd opinion.