I agree with Kathy. Some lines run lean. I have a line that does run lean, and he is still on puppy food. He is also very picky, so it's always a challenge to keep him eating. But he is on puppy food at over a year. His mother only filled out a bit more after she had the pups last year. Her sister, that has not had a litter, is still very skinny and so are the other boys.
My other line, usually around four to six months I change them over. The quality of the food, is, IMO, generally what I look at. A good quality food is just as good as puppy food, without the extra fat in it. The food they make now isn't like the food of 20 years ago.
It is best to ask the breeder, simply because they know the line and how they grow.
We fed Shaye puppy food until 6 months, started mixing it then, and when she was 9 months, we got Gemma, who was already 16 months, so we switched to entirely adult food. Fortunately, they were both on Blue Buffalo at the time - since then we've had to change because they hated the little hard things in Blue Buffalo, and it appears most of the really good nutrition was in them. Now they are on Nutro - they love it and it seems to be easy on their systems.
Nutro and Eukanuba are about of equal low quality, but at least Eukanuba doesn't have menadione, so if those are your only choices, I would choose Eukanuba. Good foods for about the same price are Blue Buffalo, Wellness, Castor & Pollux, Merrick, Taste of the Wild, Canidae, Solid Gold and Pinnacle.
dmey a good place to check is the dog food comparison chart. These are the top ones on whole dog journal:
Back T Basics
Bench & Field
Burns Pet Health
Castor & Pollux
Della Natura Commadities
Diamond Pet (Chicken Soup, Premium Edge, Professional Et & Taste Of The Wild)
Dr G's Pet Food
Dr. Tims Pet Food
Drs Foster & Smith
Natura (Calif Natural, Healthwise, Innova, Evo & Karma)
Natures Variety (Instinct & Prairie)
Perfect Health Diet Products
Pet Chef Express
Petcurean Pet Nutrition
Solid Gold Health
Tuffys Pet Foods
Verus Pet Food