Maybe if you cut the portions and space them apart to let his system acclimate to the new treat the stool issue might go away. Could be the prebiotics and probiotics don't agree with him.
They get great reviews on Amazon
Amazon
Ingredients: Potato flour, rice flour, glycerin, potato starch, natural flavor, dried kelp, canola oil, parsley, lecithin, glycerol, flax oil, yogurt powder, fructooligosaccharide(prebiotic), citric acid, rosemary extract, magnesium, dried bacillus coagulans fermentation product(probiotic).
Contains total microorganisms minimum of 14,000 CFU/gram.