It's interesting that he has problems with any other food. This must have some kind of medication in it, because the actual ingredients are definitely not the best with many fillers.
Since it sounds like he is still a puppy, you might want to consider consulting with a nutritionist to treat the problems actually causing his digestion issue. Several of us here have used Susan Davis (via phone consultation). She is fabulous and has helped everyone she has worked with. Most have used her for pancreatitis or liver issues. My Sissy was diagnosed with early stage Protein Losing Enteropathy. She has great holistic supplements and great diet knoweldge. She is definitely worth the price!!! Hope you find a solution.
Pet Health Pet Nutritionist Holistic Pet