I change brands all the time and it never seems to bother them, contrary to what the labels say. I also feed leftovers that would be wasted. Or do it the old fashioned way -- there was no such thing as commercial dog food before, I don't know, maybe 1940. Just feed table food and table scraps. Obviously, avoid a bunch of sugar and fat, though they will love some fat. Hopefully if they have a reaction it will only be a bit of a belly ache.