Starch, hydrolyzed chicken liver, vegetable oil (preserved with BHA, propyl gallate and citric acid), powdered cellulose, hydrolyzed chicken, glyceryl monostearate, DL-methionine, taurine, ethoxyquin (a preservative), minerals (dicalcium phosphate, calcium carbonate, potassium chloride, salt, ferrous sulfate, zinc oxide, copper sulfate, manganous oxide, calcium iodate, sodium selenite), vitamins (choline chloride, vitamin A supplement, vitamin D3 supplement, vitamin E supplement, niacin, thiamine mononitrate, calcium pantothenate, pyridoxine hydrochloride, riboflavin, folic acid, biotin, vitamin B12 supplement).
Hills Z/d diet (ultra one above) is a hydrolised diet; this means that the molecules of protein have been treated so that they do not trigger an auto immune response in your dog. It is an extremely expensive way IMHO of treating IBD. It does NOT remove potential allergens from the diet.Have you not thought of allergy testing your dog to identify what are the problems foods for your dog? This would mean that you should potentially be able to feed a diet which does not contain the items that cause this problem in the first place. (It would also be considerably cheaper)
Basically you are treating the symptoms of a condition but the causes which aggravate/trigger that condition have not been correctly identified which to me is always worrying.
http://www.bowchow.com/specific.html this link you may find helpful and there are also numerous IBD etc forums on the net which can give you support.
HTH