This spring I built a larger coop to increase my flock from six hens to 12+. My six hens are probably just over two years old (I got them from a local CSA) and may even be three years old. They are still in the old coop. Last week I picked up a dozen new chicks and they are obviously still in the brooder. Of my older hens, one has a really poopy butt that won't seem to clear up, and one of them is missing most of her feathers (she has been missing them since I got her. I was told she was moulting, but they never grew back). I've looked multiple times for mites and haven't seen any, but I still treated with DE. These hens free range most days. In a few weeks I'll be moving the chicks to the new coop. They won't be allowed out for awhile until they acclimate. I'm hesitant to move the old hens in with them because I don't want to transfer any issues those girls had to the new coop. I also don't want to free range them together for the same reason. Am I over thinking this, or should I keep the old girls cooped up until the new girls start laying, then get rid of them? Thanks!