Anyone have experience with Hill's Z\d hydrolyzed protein?

I have spoken about the diarrhea problems of my newly adopted FIV pos feral in the thread 'I let feral Minou inside' in the Caring for ferals section but i will post this here in the hopes of getting more feedback.
Minou has had smelly runny stools since i noticed back in August. I had him TNRed in October and he had a solid stool the night after his surgery, but then it got back to runny yellowish stools.
When i decided to adopt him, i spoke to my vet about it, and she prescribed some fenbendazole without seeing him and after a negative stool sample i had brought her.. It did not work. Then she prescribed some metrodaizole, and that did not work either.
I finally was able to get him to the vet, and he had a full  blood test which came back normal except for a slight anemia that she reckoned was due to him losing blood through his stools. She guessed his persistent diarrhea was due to IBD and prescribed cortisone. Three days later, he had a semi-firm stool, but then it was back to runny ones. So the vet guessed on food allergies and put him on Z\d. Two days later, i had to take him to the vet again cause he was dehydrated from frequent diarrhea and would not eat. He had fluid therapy and and appetite booster and put him on 3 days of rice and tuna, and perhaps some antibiotics a couple days later (which he did not get cause the vet feels we should wait and see). He felt a lot better and ate a lot, only pooped once a day (still runny) then he had a firmer one. Back to the Z\d, where he continued to poop once or twice a day very soft stools. Then 2 days ago he did a perfectly firm one, and i thought he was out of the woods, but then he had too very soft one overnight. I saw the vet when i went and got more Z\d cans yesteday, and she said to wait and see. Then nothing for 24 hours, and another soft one. And now two soft\runny smelly stools in under 12 hours.
If it is only food allergies (i suspect chicken), how long is it supposed to take for the Z\d diet to work?
He does not go outside anymore, not past the porch, and is not eating anything else but the Z\d kibble and cans, and the occasional hydrolyzed treat. He cannot get into my other cat's food.

I feel i should mention he hates pumpkin, cannot be put on a raw diet cause he is FIV pos and also cause i can't do all that anyway, and more pushy stool testing is not recommended by my vet as she feels it is very expensive but unreliable.

What do you guy think?

There are threads about Hills Z/D here on TCS: http://www.thecatsite.com/newsearch?search=Hill's+Z\d+hydrolyzed+protein&type=35 You might find helpful info there.

If it's food allergies, can you try a commercial limited ingredient diet such as Nature's Variety LID or Natural Balance Pea and Duck?

I think it takes a couple of weeks of eliminating one ingredient at a time to see if the cat improves.

Thanks for the link!

I already have my eye on Nature's V LID  venison and already spoke to my vet about it cause i think it seems of better quality than D\d. But she wants him to be strictly on Z\d for the time being, for 3 months, and then start re-introducing foods to see if there are reactions.
That's IF he has food allergies...Its my vet's guess at the moment.

My experiences with determining whether my cat has a food allergy:

http://www.thecatsite.com/t/327373/starting-cat-on-an-elimination-diet-due-to-suspected-food-allergy

The allergist/dermatologist I see says 8-10 weeks on a restricted diet is usually sufficient to clear up a food allergy, before turning to challenges.. My cat would not eat the Hill's hydrolyzed canned. One of the Nature's Variety Limited Ingredient is an option. So is the Hill's z/d, which many will say is probably one of the best options, provided your cat gets enough water in him/her. I think mine may be constipated being on the dry for so long. Good luck.

Minou was on Z/d for just a few days, and after having to take him to the vet to get subcutaneous fluids cause the poopin had gotten worse, the vet suggested tuna and rice for 3 months. That got old quick for him and his stool smelled 10x worse than the usual foul smell, so i put him on turkey and rice water with Fortiflora. He got tired of the turkey after 3 days so i gave up and put him on GO limited ingredients duck and peas, with the Fortiflora.
His stools are now pretty much formed and less stinky, but he does scratch himself some, mostly face ears and paws. It's only been 5 days though, so maybe that will resolve itself too.