I would back off the treats for now and put him on some probiotics.
See trackback to the thread about ulcers.....it includes info about dac Digestive Feed Additive
and dac Formula 911
and why they benefit the gut.
I would do a broad spectrum dewormer with praziquantal in it after he has been on a probiotic for 5 to 7 days.
Then gradually introduce your treats over a few weeks. You can use bits of his normal hay or some of his feed for enticement in the mean time.
Also remember to take at least 7 days when introducing new feed. I usually do it in parts - 1:6 new:old day 1, 2:5 new:old day 2, etc...etc.... Works out great for me when most of mine are on 7 pounds a day or 3 1/2 pounds twice daily. So I split my parts by the 1/2 pound.