My chickens eat grass.
I can't let them free-range as I'd like to (they tear up my garden too much), but I pick them 10 gallons of mixed grass, weeds, and accompanying bugs daily. They love the stuff & it balances the omega 3's/6's in their eggs.
I also give them as many vegetable and fish scraps as my kitchen can produce.
And, sadly, I have to supplement some with commercial scratch grains to be sure they get enough calories. I try to keep this to a minimum, though.