
Let him finish growing before you consider bulking him out, it's no good for any dog to be overweight and it puts an extra strain on a growing puppies joints & bones, not to mention other organs. He needs his 'bulk' to be muscle, not fat, an overfed pup is not going to put on muscle (unless you re giving him muscle-building workouts, which IMO he is too young for), the muscle bulk comes with adulthood (testosterone & genetically driven). As long as he isn't underweight (as opposed to lean) then he's fine :)
My pup is on tripe & bete complete, but not to bulk him up.