The purpose of switching to grain - free dog food shouldn't be just about eliminating grains, in fact some dogs benefit from dog food with grains. (petco.com)
Yes, there are cats that can eat food with grains without any problem but that doesn't go for the entire cat population. (tinpaw.com)
On the other hand, it won't hurt your dog to eat a high quality food with some grain in it either. (dogfoodinsider.com)