Got our RIR hens from a farmer when they were between 9 and 11 weeks old. They had been with many other hens of all ages and were all missing tail feathers. We were very new to chicken raising so we didn't know this might be a problem. That was October 2015. It is now May 2016. They are all wonderful layers. However, I cannot control the feather picking amongst them. We first tried pinless peepers --- they learned to get around them so eventually we took them back off. I am now using Blu-Kote whenever there is a bad episode. They all look like nearly tail-less wonders. There is not a single hen that does not do this to other hens either. We separated out 2 of the biggest offenders in (another coop and run we built for them). Then separated out 2 others that we also main outcasts and picked on and built an additional coop and run for them). Those four are doing well. We only have a total of 10 hens -- so six are left in the main coop with full yard access during the day. They have lots of oyster shell and also I have added a bowl of "feather fixer - high protein" within the coop along with their regular food. Nothing is working. I notice around town everyone else seems to have fully feathered chickens of all varieties living together. Ours look like a weed whacker got to their tail ends. I only have big worries when they pull a feather on somebody that bleeds -- then I treat immediately. Any other suggestions here -- and not I am not ready to part with any of my girls.