Chickens. You don't necessarily have to feed them grain. They can scratch around and get a lot of their nutrition from grubs and insects.
Obviously I'm not talking about factory farming here, but it wasn't that long ago, my own childhood in fact, when every family I knew had chickens in a pen in their backyard.
The saying, "running around like a chook with its head cut off" has real meaning for me because, after my father had beheaded the poor chook chosen for Sunday dinner, it was my job to catch the bloody thing.