My chickens are almost a year old (8 hens, 1 rooster; different breeds). I have had them all since they were chicks and they have been very healthy and lay lots of eggs since they started laying. Several months ago I found my rooster laying on his back and he couldn't get up so I uprighted him. After that he seemed to go downhill. He started losing his tail feathers and then his whole backside just started looking bare. Then, he started having these episodes where he can't go from sitting to standing very easily and these spells have increased recently. The hens have been doing great all the while until about 2 weeks ago or so and I noticed some of them have started losing butt feathers. One has started losing on the back of her neck as well. I have inspected them, best I can, for mites and have found none on them or in their bedding, which I just changed 2 weeks ago. A little about their living space: they have a 100 square foot run and a nice big house to roost in with several laying boxes. They are eating Layena. They have been out of the run to free range several times, but not lately. We have several dogs around that periodically make their way through our yard and they do not like chickens. Any thoughts on all of this? Thanks so much to anyone who can offer some advice.