I've recently done quite a bit of research about historical chicken-keeping between from the 18th to 20th century when commercial feeds were produced and sold in the 1940s. I've read a number of chicken and livestock manuals from about 1820-1920s.
In the late 1800s to the 1920s, poultry was expected to produce about 100 - 120 eggs a year. The most common farm and backyard breed was the white leghorn which was lighter and slimmer than today's leghorn.
Feed was non-existent. Chickens were set loose to forage but usually had farm produce and livestock feed and dung to forage from as well as fields, grass, weeds, bugs, fallen fruit, etc. Farmers likely grew some kind of grain which was also thrown to chickens, mostly over winter.
During the very late 1800s and into the first and second World Wars, chicken keepers were encouraged to use more "scientific" feeds based on a balanced diet (as was incredibly minimally understood at the time - vitamins were only discovered around 1912) which was basically a morning feed of a mash of ground grains and meat meal, oyster shell, etc. with an afternoon feed of grain, or a mash made of culled produce or kitchen scraps cooked down with corn or wheat bran in the morning and grain in the evening.
During WW2, UK rationing allowed for some chicken feed with kitchen scraps being the rest of the chicken's diets. In the US, farms just let the chickens out to scratch through cow patties, eat fallen livestock grain and pretty much had access to everything but the fenced garden, made to keep chickens out rather than keep them contained anywhere. Scratch or leftover field corn was thrown out at the end of the day to get chickens to come back home to roost.
The breeds were lighter and more able to avoid predators, roost in trees or barn rafters, though they laid fewer eggs. But when you are not spending anything, or much of anything, having more hens to lay is the obvious trade-off.
Chickens left to nature on the farm will eat about 1/3 of their diets as grass and weeds, 1/3 as animal protein (mainly bugs, snakes, mice, but also butchering waste, excess dairy as well), and 1/3 seeds (grass, weeds, sunflower, millet, spilled farm grain, etc.).
People serious about owning producers culled flocks at 2-3 years. Small farms, mountain people, backyard homestead flocks, and generally poor folks kept their hens as long as possible and let broody mamas tend the new generations - kept all the chickens they had as they needed all the eggs they could get and really old hens and roosters made satisfactory stew.
