Do a slow switch using 1/4 new food mixed with 3/4 old food each meal for about a week. Then go 1/2 and 1/2 for a week, then go 3/4 new to 1/4 old for another week before giving him 100% new food. This is important because bullys have very sensitive tummys and too quick of a change may upset his tummy. If you notice soft poo while switching, back up and reduce the new food a little for a few days so his tummy can catch up to the switch. Another thing that helps during a switch is to add a tablespoon of canned pumpkin to the mix *not pie filling but canned pumpkin*. Once you switch his food give him a few weeks on the new food and note how it has helped or not, but it takes a few weeks to get the old food out of his system. It can be a long process but is great when you find the right food..... Fromm Beef Frittata was that right food for Princess Gracie.