Hi Josh S-
Unfortunetly, this puppy formula you are using is not fine tuned to suit the needs of a growing large breed puppy, so I would recommend another food.
Firstly, he should be taken to your vet and examined to make sure that if he was truly malnouished as you say, there is not an underlying condition (intestinal parasites etc) that would be causing poor appetite. I would not rely on the shelters vetting personally.
Once medicial issues have been ruled out, I would move him to Pro Plan Large Breed Puppy hard food. Haven’t known a dog to reject Pro Plan and it is highly digestable, so it will be easy on his stomach.
