Of course how well they do with letting them forage for part of their diet will depend on the quality of the forage. The model I'm using is the small farm I grew up on. If they have enough different grasses and weeds, grass and weed seeds, various creepy crawlies, and dead vegetation or other animal poop like cow or horse to scratch in they can be extremely self-sufficient. Predator pressure plays a big part too. If you can't allow them to forage because of losses to predators then it won't work.
We never fed our chickens in the good weather months. They fed themselves. In winter we did supplement their feed with corn we'd raised ourselves, but we didn't have a lot of snow so even in winter they found a fair portion of their food. Some of that was from the hay we fed the cows and horses or by scratching in the poop. During the good weather months our kitchen wastes were fed to the pigs but after we butchered the hogs in fall the kitchen wastes were thrown where the chickens could get to them.
We had a barnyard mix of various breeds that had some game mixed in. Every five or six years Dad would bring in a dozen Dominique or New Hampshire from the Co-op and bring them into the genetic mix, keeping a rooster from those breeds so it was not just pure games.
Ours were not show chickens. You need to feed show chickens special to get them that big and the feathers that shiny. They were not raised for commercial purposes. They were only to provide eggs and meat for a family with 5 kids. We ate eggs for breakfast every day of the year. Even when Mom made pancakes I'd usually have an easy over egg on top. We followed the same pattern that had been followed on small farms like that for thousands of years. The hens would hatch out and raise chicks in the spring and summer and we would eat a lot of chickens late summer and fall to get back to the numbers we overwintered. The chickens were not huge lumbering beasts but Mom could get a meal for five kids and two adults out of one of them. Neck, back, and gizzard were added to the normal parts you can get at KFC. It is surprising how much meat you can get off a neck if you really want to. We never butchered and preserved chickens. None went in the freezer. When Mom wanted a chicken she'd tell me and I'd go catch one, kill and pluck it, and give it to her. They were not aged for days in the refrigerator, she cooked it that day. And they were delicious. We'd have the numbers of the chickens down to where Dad wanted them about the time we butchered the hogs which provided meat for winter, spring, and early summer. Our calves were all sold, not eaten, as we needed the cash. Chicken and pork were our meats with occasional fish we caught or game we shot as additional treats.
Of course it depends on how rough your winters are and the quality of forage but lets do some quick math. How efficient is it to get eggs and meat for your family when you provide none of their feed for the good weather months and just provide corn that you raised yourself in the bad weather months as a supplement versus buying feed for them year around. That math is not real hard for me to do.
Most people can't do this. They don't have quality of forage, nice enough year around weather, or the predator pressure is just too great. But if you can allow them to forage for a portion of their food you can cut your feed costs.
