FYI Free range as used in backyard flocks like ours does usually mean letting the chickens out into an area not enclosed by a fence. It is the USDA that gave it such a belittling meaning.
I understand the the USDA defines free ranging as a bird having the ability to go outdoors. This does not mean the the bird actually goes outside.
I would use words like grass fed or pasture fed or pasture grazing. You need to bring in the fact that they have access to green forage, not just a...