I have 10 hens and one roo. I have one hen who has lost her back feathers and neck feathers. I assume it's not mites since she is the only one who looks this way. She looks like a typical "over mated" chicken. BUT,,,,,, yesterday I noticed when she was taking a phoo that all her feathers are missing around her butt too. Is this normal for an over mated chicken or should I be concerned???