My grandfather was born in the late 1800's and died at the age of 100 about 20 years ago. He was a farmer all his life. I asked my dad recently what granddaddy fed his chickens, thinking he'd say he just threw out corn or scratch, but was surprised when he told me that granddaddy fed the hens a laying mash. So, not all old farmers just feed corn.
I think the time in a chicken's life when proper nutrition is most important is when it's growing like crazy as a chick. I've seen stunted chicks who were fed only scratch as babies. I've seen them stunted after someone bought them from me, after they'd been on proper high protein starter feed here, then for the next couple months of scratch alone. The difference in the one I kept vs the ones who left here at six weeks old was convincing enough for me. Hens need calcium so you need to supplement that, especially if they aren't being fed layer feed. Chickens can survive on very different diets, especially if they free range and find food on their own, but some don't really thrive unless fed age/function appropriate feeds.
I think the time in a chicken's life when proper nutrition is most important is when it's growing like crazy as a chick. I've seen stunted chicks who were fed only scratch as babies. I've seen them stunted after someone bought them from me, after they'd been on proper high protein starter feed here, then for the next couple months of scratch alone. The difference in the one I kept vs the ones who left here at six weeks old was convincing enough for me. Hens need calcium so you need to supplement that, especially if they aren't being fed layer feed. Chickens can survive on very different diets, especially if they free range and find food on their own, but some don't really thrive unless fed age/function appropriate feeds.