Hi Christine,
The soft stool could definitely be the result of a food intolerance. My dog with food intolerances gets soft stool from lots of things, especially flax.
The first thing I would do is put him on a limited ingredient with an appropriate Calcium level for a large breed puppy; ie: Nature’s Variety Instinct LID Rabbit.
Loose or even soft stool for a prolonged period is a problem that you can’t allow to resolve on its own without taking action. I would change the food and add canned pumpkin to his food to help firm the stool and ease the transition to a new food.
