I feed my chickens a feed that has a small amount of corn in it. I notice when they eat the grain I throw out for them, they always eat the corn last, if at all. They much prefer the other grains. They are free ranging and feed on grass, bugs, worms etc
and seem to eat anything in sight, except that they don't touch any plants that aren't good for them or that can harm them. If they would rather not eat the corn maybe they know something.