Alot of feed mills use supplement when making feeds, it's a pre made/ mixed 40+ % protien mix. Our local feed mill can mix a starter/grower or layer ration - there are 2 different supplements for each mix - the layer has more calcium and isn't good for growing birds.
They mix the supplement with ground corn to get the right protien level you want - for our layer ration we also add 150 pounds of oyster shell per ton of feed.
Note the last 2 ingredients in Walters feed mix
Bacitracin - an antiboitic
Histostat - an anti blackhead
If you are claiming organic/natural you would not want to use those two.
For the protien level we feed 28% game bird starter for 8 to 10 weeks
20% grower up to 6 months of so
After that they go out with the flocks and get a 16% layer, supplemented with fresh greens, boiled back eggs, plus what they can forage.
We don't raise ours for the Thanksgiving market so we don't feed for max weight gain in the shortest time. If you wanted to do that the recommended is keep them on a high protien until slaughter.
Steve in NC