When considering protein there is a difference between animal and vegetable. Animal is a more complete protein. Sorry I don't have any science based references or peer reviewed articles to back up my claim but I believe my flock is healthier because they free range and eat a lot of insects and other small animals. Most feeds contain no animal protein. During the winter months I will supplement feed with some meat table scraps. My hens lay all winter. I did notice that Purina is trying to fill the gap in non animal protein feed by offering a Free Range feed that contains black soldier fly larvae. I'm going to include in my winter feeding.