We've had a LOT of stomach issues and tried a ton of different food.  We were drawn to Merrick based on them touting it was for "sensitive" stomachs and that you can interchange the flavors without any tummy problems.  My dogs are crazy about it, but i wouldnt suggest changing up the flavors TOO often, we did notice some soft stools but we are not sure if thats the cause or the nylabones that we've now taken from them.  I've noticed that since we've given them so many different flavors, they seem to be annoyed if we serve the same one more than 2 meals in a row.  They were also spoiled with the wet food so they dont love the dry food as much.  But we are 100% happy that we found a food that we have not had any tummy issues with and that we are able to give them a variety of flavor.  Be advised, one flavor has a full bone in it, but it is soft enough to eat (we havent tried it yet) and the lamb sausage one is really tough and you'll have to cut up the pieces smaller.  Good luck!! 
