I would try sprinkling Parmesan Cheese (from the green can) on his food as that can be very enticing / appetizing for dogs.
Otherwise, have you tried frozen raw or freeze dried raw? May be worth a try...
__________________ ~ A friend told me I was delusional. I nearly fell off my unicorn. ~ °¨¨¨°ºOº°¨¨¨° Ann | Pfeiffer | Marcel Verdel Purcell | Wylie | Artie °¨¨¨°ºOº°¨¨¨° |