I’ll repeat some of what Bill said. I know that many people look for the BIGGEST lab they can get, but many more are beginning to understand that bigger is not always better, and often you get additional problems in that BIG package. Just a sided note… if breeders intentionally breed for size of lab as the primary selection criteria, they are risking the introduction of many other genetic weaknesses into their line. Familial proximity shoud be the primary consideration, functionality the second, temperment the third. Size should be the fourth consideration and then other appearance factors. Any failure in the first three considerations should prevent a breeding. Deductions in the other considerations is a matter of personal taste or preference.
If you start selecting for appearance and size above the other factors, I think that you’re asking for trouble. Back to the topic of feeding your dog. Many HIGH quality foods are available with HIGH nutrition. (Some premium foods are not very good and have sugar and less than quality ingredients…research them before you buy) Accelerated growth in large breeds can cause significant health problems and even pain for your furry friend. If you think that your dog either has a potential for displasia, OCD, or other joint problems…consider switching to a less than premium food after about three months. Go back to the premium stuff after 10 months, but make sure it is ADULT premium food. The size of your dog is more a function of genetic input than of food it eats.
A dog that is destined to be a LARGE dog, will simply be a LARGE skinny dog if it is not fed enough in quantity. Let me qualify that before I get into to much trouble. If you feed adequate nutrition, (run of the mill grocery brand food) to a puppy destined to be BIG, he will get big. If you feed premium brand puppy food he will get BIG faster. He will fill out faster. He will carry this additional weight on not yet fully developed joints. Ligaments and Tendons may not grow as fast as the bones (ouch). The ultimate size will be the same. I feed Iams (the dogs like it :>) but I’m sure any of the top quality, premium foods are good.
I also switch my pups gradually onto adult food beginning at 4 to 6 months of age. It’s important not to let puppies get fat, as carrying the extra weight is even harder on their developing joints. I have some good articles on nutrition and OCD if anyone is interested. I think I can attach them to files going to personal e-mail rather than bomb the whole list. My Griffon pups are now about 5 months old, and they are eating Iams chunks. They are doing well on it, and have hearty appetites. Against my own rules they are a WEE bit chubby, because we have been getting 40 below weather, and the snow is over their little heads. They are really game, though, and plunge along sniffing everything in sight. (Or out of sight, as the case may be when they disappear in a drift.