We have 6 2 yr old red sex links who lost many feathers this past spring/summer. I suspected the back/shoulder feathers were due to the aggressive rooster. He's gone now. We have about 30 new hens and 2 young roosters. None of the new hens are missing feathers. Of the older hens, 3 are fully feathered now and 3 are still missing many feathers on the back, belly, bottom and legs. They don't seem to be growing many back and I have no idea why they'd be missing on legs and belly. Any suggestions? It is starting to get below freezing some nights. They have coops and heat lamps, but I worry about the ones without feathers freezing.