Julie...remember, Vets aren't always up on nutrition. Heck, they come out of Vet school seriously lacking in this area, and as the science moves forward, they don't keep up. It's hard for them to keep up with every little thing....and nutrition is far down on the "important to know" ladder (probably non-existent), for them.
In this case, you might want to consider the advice of other breeders who have used one method and have had great success with it. Talk to a lot of them and see if you get a consensus.
I've told my Vet things that he knows absolutely nothing about. Then months or years later, he catches up. Especially when it comes to nutrition, and Newf-specific information.