I have a 100% free range flock of 15 birds (14 pullets, 1 rooster).
They get a square horse feed scoop of 10% protein scratch grain in the mornings, some days I mix it 1/2 cracked corn and 1/2 scratch. It's just a treat for them. They also get all household scraps. I put out oyster shell, and that's all they get on a regular basis! They forage around our 5.5 acres, sometimes cross the outer fence and go to the neighbors but not often. It's almost all ranch land around me, very rural. Oh, when I feed the horses AM & PM they stand around and pick up any grain pellets they drop, my old mare in particular drops enough that the chickens feel it's worth their time to stand around and beg!
They are doing great on primarily just forage. I have Barred Rocks, Rhode Island Reds, Ameracaunas, a Buff Orpington and a Jersey Back Giant.
I just turned my young (6-10 week old chicks) flock of replacement pullets out to free range during the day. They went from eating a big pan of feedd in the morning (1/2 chick starter, 1/4 cracked corn, 1/4 scratch) and 1/2 a pan in the evenings to not even finishing the morning feeding now that they can range. My older layer flock has access to that same pan of feed. They all pick at it, then go forage! The replacement flock consists of: Barred Rocks, Black Australorps, Rhode Island Reds, and Black Sex Links.
The only birds I have that are really, really happy to get processed feed are my Freedom Rangers. They will go and forage (just in a tractor right now), but would rather stand in front of a feed tray!!
I've been very, very pleased to see that my layers will pass up the 'dead' commercial feed in favor of 'live' forage (plant, bug, or what ever else). I get really nice, huge eggs and lots of them! Nice fertile eggs too. I've had three hatches from my eggs this year, 2 here at home and one from eggs I gave a friend. My last hatch was under a broody hen.... 11 chicks 8 of which are pullets (black sex links)!!
Liz