I’d switch the pup immediately. He already has loose stool, so a quick switch wouldn’t hurt. Something he’s eating doesn’t agree with him and the longer he’s exposed to it, the more damage that it can do to his gut. It sounds like he’s been eating the Blue Buffalo for at least a little while, is that right? A good I found that was very easy to make a quick switch to is NutriSource. I used the Adult Chicken & Rice when I needed to make a fast switch with a pup of mine.
I’d pay close attention to the ingredients in what you’re feeding and your pups reaction to the food in an effort to try to determine the offending ingredients. I ended up with a spreadsheet with one of mine before I figured out that he can’t eat fish in any form, chickpeas or garlic (garlic, of all things).
Personally, I wouldn’t feed any Blue Buffalo products.
