Question about Dog Food for puppy

Hello everyone!
So recently I adopted a puppy from a local puppy rescue. He came from New Mexico high kill shelter and I saw the rest of his litter and they all looked completely different. One had Berner coloring, while 3 others had all white faces with brown markings...? They didn't have HUGE paws but they are big. Oh and my boy had Saint coloring. Very odd!
Anyways so not huge paws but I am thinking larger breed? BUT I am worried that since he is such a mix and could possibly be BIG that I shouldn't be feeding him large breed puppy... you know with Giant breeds feeding them adult food is what to do as to avoid joint problems and growth problems with too much er calcium.. protein? Not completely sure on that piece.
ANYWHO my question is I am feeding a good quality large breed puppy... wondering if I am going to mess him up his growth or what really to feed a MIX breed pup when you just have no clue!??
THANKS!!
Maggie Mae
ps. pix of my page gotta put new ones he is getting HUGE

A very good friend wrote this thread for dogster.com. I would check it out if I were you :)

http://www.dogster.com/forums/Food_a.../thread/663911

Recommend keeping puppy on large breed formula and NOT adult as large breed, even for giant breeds (which are still large breeds) have the correct ca/ph ratio. Adult food usually has way too much cal/ph in their foods.