I am not an expert on anything much but have an observation. My chickens have been free ranging during the day for a few months now. They love grasshoppers, wild grass seed heads, scratching in the neglected flower beds and cleaning up under the bird feeders - 4 years of spilled seed: millet and other small grains plus black oil sunflower seeds. They are doing quite well, are glossy, active, happy and the eggs are fab.
I think that given enough space and choices, the chickens will not eat what is not good for them.
What do more experienced chickeners think???