Bare bottomed hens with red skin?

[Debtalley]

i have 8 chickens in a big coop, about 9x8 and an 8x11 or 12 run. We have had them since last easter and nothing like this has happened, but now a few of them look like this: with bare bottoms and red skin. There are no roosters, and a variety of breeds. Also, i have a brahma, with feathered feet. She has blood on her feathers and some of the feathers on her feet are plucked and there is blood in the holes where they were. We let them free range for an hour or so before sun down, but since we lost one to a hawk and it has been winter, they havent been out in a while. Today i cleaned their coop and put DE on the edges and the perch, as well as the nesting boxes. I also checked for bugs but didnt see anything. Im thinking that maybe they need to be let out more, they have mites, or theyre molting, or maybe just pulling feathers out. How about you guys? Im really worried for them it looks painful, ecspecially the one with the bloody feet. They all seem normal, but im just really worried!

I have same problem and have tried powder, ointment and spraywith no results