I have a 2 year old mixed breed (terrier, beagle, ??) . We have been feeding purina's moist and meaty dog food.  He likes it soft, not wet, or (hard) dry.  Over the past few monhts, he is having a problem with scratching A LOT. The vet said to change is food, he more than likely has an allergy.  PROBLEM- we have tried to change his food and he WON'T eat. He barks at us, he bites our sleeves or pant legs, to let us know he is hungary.(he has always done that).  What can we do???