I have a flock of barred rocks that I have noticed loosing some feather's. It first started out as the "over mated" look on the back of the hen. Then I noticed that the roo was loosing tail feather's and was really red around his bum. The one hen has lost all her tail feather's, and a couple more hens look like they are starting to loose a few. I have treated with Ivomec about 6 months ago, and I have also dusted them all about 1 month ago. They are all acting fine eating, drinking, pooping, doing the normal chicken stuff. What could be causing this? It is because they stay in the coop and run all day?