I change a lot because I want to try new things. Or I find out that something might work better. Jack was on Earthborn bison but it had a lot of calories with being high protein/high fat. He's heavy. I also had to weed out anything with chicken or lamb in it. So through trial and error I found something now that I think is lower in calories and is made with ingredients that shouldn't aggravate his seizures. I tend to prefer Pro Plan (good middle ground and I am in their breeder program so I save the circles for stuff), but Grace needed to lose weight too and I didn't find that she was doing that on PP's weight control food, so she's been trying Fromm's whitefish and Evanger's whitefish. Then I'll change it all again because I want them to rotate their protein source. I don't think it's good for them to eat the same thing day in and day out. I don't really apply the "wolf" theory to dogs much, but wolves probably don't eat rabbit every day. Nor should our dogs eat chicken kibble every day. I certainly would be pretty annoyed if all I got 3 meals a day were Cheerios. Variety is good for the diet.