If you look at the analysis on the tag on the bag of feed, the only significant difference in Chicken Starter, Gamebird Starter, Grower, Flock Raiser, Developer, Finisher, or whatever combinations of these you see is percent protein. Some of these have other names with certain brands or at certain mills and some may have slightly different protein levels but protein is the only significant difference.
An example. One combined Starter/Grower is called Starter/Grower and is 20% protein. Another is called Start & Grow and is 18% protein. Both of these can be fed from hatch until you switch to Layer. Or you can keep feeding either of these and offer oyster shell on the side even when they are laying.
If I remember right, Fred uses a 18% protein Layer. I use a 16% Layer when I don't have a mixed age flock and can use it.
If you look at the tag on a bag of Layer, it will have a percentage protein somewhat close to Grower and it will have about 3% higher calcium. That extra calcium is there for the hens to male the egg shells. Too much calcium can harm growing chicks. If a hen is not laying she does not need the calcium in Layer and growing chicks should not eat it.
Before you ask, we do not all follow the same feeding regimen. The normal one often recommended is to start them off with a fairly high % protein feed, after 4 to 8 weeks (whenever your last bag runs out in that window) switch to a lower % protein feed, then when they start top lay, switch to Layer. When you switch from one to another does not have to be very precise, just as long as they have access to extra calcium when they are laying. Like Fred said, I offer oyster shell on the side to cover that.
But lots of people keep them on a higher protein diet all their life from hatch until they are done, like a 20% Flock Raiser. If all I can find at the feed store is Grower, I'll start them off on Grower. It doesn't hurt them. if you are growing them commercially or for show, a feeding regimen is a lot more important that just for a regular backyard flock. People get worried about feeding all the time when they don't need too. Unless you have a special need, and these people should know who they are, % protein is not that important.
