Back in the Olden Days.......................
Grandma & Great Grandma never fed their birds, ever, cept some scraps.
There was no such thing as trips to the feed store (or grain mill) for "chicken feed"
LOL
The pigs got the scraps (and the dogs) and the chickens free ranged, and sometime in the afternoon, these women would walk out in the dusty yard & toss scratch to the birds.
That was the only grain the birds got.
No soy protein, no marigold extract.
No vitamins or amino acids..........................
These women also did not have incubators, (or Silkies !) and the birds had to be broody on occasion to keep their flocks sustainable.
There was hatcheries, even way back then.
But not many could afford to spend money every year on chicks, especially during the dust bowl & the Great depression.
My Dad had chickens even when I was a baby, and we had no hen house, the birds slept in trees, and free ranged, and were given a scoop of scratch a day.
Finding eggs everyday was a hunt !
So, moral of the story is, I think chickens were fine 100 years ago living on dirt & scratch, they'll be fine now.