I use fromm gold large Breed puppy for my newfoundland it has been fantastic and she loves it. I also use a rotation of canned food and fish. I would definitely take him of purina you said your vet put him on an antibiotic and wormed him both of those things can cause loose stool. Antibiotics kill the good bacteria in the gut as well as the bad you can add a probiotic to his food and some all natural pumpkin for the next week or so if his stool is still loose. Good luck with fromm the LBP has an excellent rating the LBA has an ok rating although I am not sure why.
