My male bulldog also gets diarrhea when he eats any canned food. May be the preservatives putted inside make it. When one of my dogs has diarrhea I gave them "Smecta". It's a human diarrhea medicine and it works.
Try with home made food but may be chicken is better then lamb. Have in mind that any change in the food cause diarrhea first few days.
I hope it will work))