Ostensibly, the grower feed is lower in protein in order to slow down sexual maturity in pullets so they are slower to come into lay and hopefully, avoid some reproductive issues that plague hens, especially hatchery hens, in my experience. It is to be fed in a defined period, after you stop the starter and before they lay, though I've never used grower.
I feed 22% layer to my heritage line birds from breeders, which tend to be much larger birds than hatchery birds. It was recommended that they have a higher protein level. All chicks get 18% starter/grower until laying age, no grower around here unless I buy at TSC, which I avoid for the most part.
My "scratch" is actually a 13 grain cock conditioner which has 16% protein on its own, but anything they get other than layer will lower the overall protein content unless it in itself is high protein like mealworms or eggs, etc.
