Hi Simon, I just checked the ingredients for Iams Puppy, Beneful, and Canidae All Life Stages. Iams and Canidae both have prebiotics, and Beneful does not–that is your answer. Iams has FOS (Fructooligosaccharides) and Canidae has inulin (usually chicory root) as a prebiotic and papaya and pineapple act as digestive enzymes. After reading the way you say Moose reacted to Iams, and now the change in behavior with Canidae, I am 100% certain that he has a sensitivity to prebitoics. It took me two years to figure out that prebiotics would set Lucy off. FOS is the worst, but any prebiotic causes her ears to become extremely sensitive to sound, and she gets aggressive because she does not feel good and her gut hurts. FOS also caused her coat to become dull and excessive shedding. You may find that Moose has trouble with any food that has high soluble fiber (prebiotics are classified soluble fiber), such as the grain free foods containing tapioca starch.
I know the other people think the behavior change is coincidence and it is not the food, but I have lived through this and the food is the problem. If you want to look for a food other than Beneful, stay away from anything with probiotics because they will usually have prebiotics.
