I am by no means an expert but here's a few thoughts. Is Nutro a lamb based formula? I know my friend's pup just does not do well on a lamb based diet.
I personally find Bil-Jac Select to be a hair on the high side in protein and fat but so far our boy really does thrive on it. We keep him pretty active and are extremely cautious about monitoring his weight. We feed him less than the manufacturer's suggested serving size for his weight but as I stated earlier, we do supplement with carrots, green beens, brocolli etc as fillers in his diet.
It's extremely tough sometimes to decide what to feed your best friend. So much of the literature and websites out there tend to contradict one another so much it's just a cluttered mess. Basically, I believe you find a food that has the least amount of "crap" added into it, uses human grade ingredients, and then play around with a few different types until you find what works best for your pup.
Sorry for a lack of specifics, maybe one of the breeders or someone with more newf experience can help you more.
One other thing for you to bear in mind is that our boy P.J. is a rescued Newf/Lab mix, so maybe someone with a purebred can offer better diet advice.
I've rambled too long already,
Good Luck in the quest!!!!