this was several years ago, but my boy lost weight, lost muscle and was still itchy and had skin issues. Too low in protein etc. I would try a sensitive skin food like Eukanuba or Proplan.
I used that for a while with one of my dogs till we could rule out exactly what her food allergy is (corn, chicken, soy) and then she spent some time on Kangaroo and Oat but at the price of kangaroos it would be cheaper to just feed her my pay check so now they are all on natural balance fish and sweet potato with good results.
the Z/D was ok for allergies, but i felt like she wasn't really thriving on it, coat dull, just not her usual bouncy self. ok for the short term but not for the long run