For what it's worth, my IBD dog (Minnie, a poodle) has been well controlled for years on a suitable diet. The initial bouts of HGE, which occurred before she was three, were so bad I almost lost her, and she was scoped (two types of severe IBD related at least in part to food allergies) and put on a slew of meds, including the maximum dosage of pred. She was also given a limited-ingredient novel diet. We were able, in time, to eliminate the meds. Now that she's 13, she's gotten a bit more fragile, and is back on misoprostal.
Some years after Minnie was scoped, we tried food allergy testing. Although it has a bad reputation, it has been very helpful for Minnie and others (one suspected colitis, some prone to soft stool) here at GITroublesRUs.