One of my rirs is missing feathers on her back like the rooster has been with her too much but he hasn't. She's the only one with this bare back and what also puzzled me is her head is missing its feathers too. All 27 of my layers moulted last fall and everyone grew back normally but not her. Any ideas?
That REALLY sounds like your rooster is overbreeding her. The missing back feathers are one clue, but roosters also grab the feathers on the back of a hen's head/neck during mating to help keep their balance and they can pull those out too. Roosters do pick favorite hens, so maybe he really is overmating with her even if you aren't personally seeing it happen.
The pattern of feather loss does sound like "rooster rash". Or it could be other hens picking new growth out, and she never did recover fully from molt and the rooster and the other hens. Wouldn't be a bad idea to sequester her into a dog crate within the coop if there is space. She isn't sick, so it would be best if she could have some healing time but remain within eye sight of the flock. Out of sight, out of mind for chickens, and the re-introduction could be hard on her. Applying blue kote would reduce the interest from the other birds, but if the rooster is also the problem then she would need physically removed from his attentions as well to let the feathers grow back. If they're plucked prematurely too many times, the follicle can be damaged and new feather growth inhibited. The other option is one of the hen saddles. A rooster would affect the feathers on the flat part of the back behind the wings, and the feathers at the base of the skull, then on down the neck.
