We have 15 chickens that are free range during the day and are in their coop at night. About a third of them have red, inflamed behinds. This has been going on for quite a while. We tried dusting them and their area. We don’t have a rooster, we don’t feed a lot of scraps. Their coop is cleaned regularly and bedded with pine shavings. They seem happy and are laying well. But those butts can’t feel good! Help?!