I have five hens, two brown leghorns and three red sex-link. They started losing their butt feathers a few months ago, and I have two girls with bare-naked butts (from the vent down to between their legs), and can see signs of more nakedness in the others. I have dusted both the coop and the girls with poultry dust in case of mites or lice, see no evidence of pecking and no bleeding. They have a flock block to pick, and get zucchini and/or squash every day, plus millet and scratch grains as a treat. I was letting them free- range, but they started wandering too far into the woods, so I have stopped that for now. They are otherwise healthy and give me eggs every day. I'm concerned about them with this very cold blast we are having. The coop is draft-free, but not heated. The bedding is dry and thick. They roost together on one of the rafters and on a platform by the window. I may keep them inside the coop the next few days while it is coldest and not let them out into the run (covered with plastic to keep out the wind). I did buy a small electric heater, but it may not be big enough to do much good in the coop. Will they be OK without additional heat in the coop? Is the feather issue a form of molting, or something else? Do I need to put something on the exposed skin to keep them from freezing? Input and advice welcomed and thank you!