Oftentimes switching foods abruptly will create "digestion issues". It may be eased if you combine new and old foods together for a week or so before you officially start the new food.
Personally, I would add a 1/2 teaspoon of pure pumpkin to the food to help settle his stomach. My local WalMart sells it on the baking/spice isle it for ~$1USD. Do not get "pumpkin pie mix" as there are seasonings that can kill(?) your pup. Pure pumpkin, however, is a very healthy addition to their diet.
There is a lot of pumpkin in the can! I recommend putting small dots of it on a cookie sheet, then freeze it for an hour or so. Store them in a zippered freezer bag and thaw out a few at a time (as needed). Or, toss them in the dinner bowl frozen.... something I've done recently which "doodle" seems okay with.