I have a 4 year old male German Shepard (white) as he has pretty much been on the same food for about 3 years. I feed him 4Health Grain Free for Large Breed dogs. Is it a good idea to switch dog foods every so often? Maybe not brand but the type of food? He has been having more loose stools over the past couple of months. Nothing too bad but just not as stiff as normal. Also he seems to have diarrhea after really long walks. I have been thinking about switching foods. A couple years ago he was on Taste of the Wild Bison, but it seemed to give him some intermittent diarrhea. Anybody else use 4 Health Grain Free?