[Anonymous]

I would ask your vet for a referral to a specialist or call the veterinary school in your area. What is causing the IBS, allergies?
Prednisone is a steroid, good for short term to get things under control, then taper off. Not good for long term, bad side effects and other health issues could occur.
Best to get to the root of the problem, now.

I would keep his diet simple, feed him as usual (twice a day) or whatever your vet is recommending. You don’t want rapid weight gain.