don't let yourself "overthink" what to feed your chickens.
I feed strictly finely ground corn and oats.
50/50 .
I have been accused of abusing my chickens with this formula.
so be it. I still hit 100% egg production regularly . I have even hit 100% production when the temperature was minus -20F with no supplemental heat..
do what works for you..
I do not feed oyster shells. I do feed egg shells when they are available. usually mixed in with the table scraps I feed..
when I was a kid, we didn't have crumbles, that I know of.
everybody just tossed out oats for the chickens. or corn or barley or wheat.
Did you mean that layer crumble didn't exist or your family didn't feed it? Wasn't sure. My father died two years ago at 94. His father was a farmer who lived to be 100 and died in the 1980's, had Angus cattle, mules, hogs and raised broilers plus had his own flock for eggs. I didn't remember, so I asked Dad what his dad fed the chickens. He said layer crumble. That was in the early 1900's. I could not recall, being a child when we were on the farm. I think that folks who don't use layer crumble or pay attention to the protein content, as we see on old movies where someone just tosses out something in the yard for the chickens, no feeders in sight, has to do with the other livestock on the farm that the chickens glean from, picking through feed of other animals, the poop from the cows and such, and they had lots more forage than someone may in a 1/3-1/2 ac lot.
I guess my point is that people sometimes get chickens and they feed them like they see in the old movies, thinking that is adequate and then, they wonder why they have no egg production (not meaning you, just musing here) or why their birds' feathers don't shine or look ratty.
I don't have hatchery birds and my heritage lines and breeder lines are larger bodied birds. They get 22% protein feed that contains porcine (animal) protein. I have a scratch mix that I use sparingly, which has 13 grains and 16% protein by itself, so if they eat too much of it, their protein levels are not too far down. They all get to free range on a rotating basis, but now, there is little green out there anywhere, of course. I do not do "fussy" feeding methods like fermented feed and actually, am not at all for it (don't start on me folks). We have a simple management style, no grinding of feed, just good quality feed for the age and function of the bird.
Chickens will
survive on many different diets. They may not thrive on some. The hens may lay infrequently as well. And if the diet is inadequate when they are fully feathered, then when they are molting it is then
woefully inadequate. I don't push them with light after so many hatchery hens died of internal laying/egg yolk peritonitis/cancer. They are not machines, they are animals whose bodies need to recharge, sad as that is for our breakfast tables. JMHO.
