Chickens loosing feathers

Hi, I have one chicken which loosed long time ago feathers on her back, but the situation were stabilized fast. She was in a good health. But 2/3 days ago, she started again to lose some. Specially around her rump as you can see on the pictures. Is someone know what can be the origin of this.

Moreover, I noticed in the same time, few other chickens were loosing feathers too at the end of the back. I have four rooster  for twenty chickens and four geese. Rooster are often in competition and maybe harass too much the chicken plus the geese are time to time aggressive to the chickens. That could be one of the reason or maybe not. Maybe there is a connection with the other chicken. Tell me what you are thinking about it.

Thank you for your answers!

Is that bright red skin their normal color? If not, you could have mites. A rooster would have clawed her back and bit the back of her head if she had been ridden too hard. These show no signs of that.
This looks like irritation to me, but that is only a guess on my part. Have you dusted for mites in their coop?

That hen may be being mounted too much by roosters as suggested, even without scratch marks, but Michael could be right about mites also.

These things may be hard to diagnose, but my friend swears by smearing the red areas with petroleum jelly and finds that it helps the bird heal, regardless of what started the problem.

I do put diatomaceous earth in my nest boxes to help with mites.

Jay Angler wrote:..but Michael could be right about mites also.

😂😂😂 If I'm right there won't be anyone more surprised than me! 🤣🤣🤣

Howdy!
I'm thinking it might be several things going on at once.
Yes, she may be a favorite for the roosters and that would cause treading damage. 5 hens per rooster is a lot for large breeds, and dominant roos will make a point about it. (I had 4 roos on my 20 hens for a brief time. I had some hens turn up like this. so I reduced the number of roosters.)

I think some of the red could be sunburn, in addition to a possible pest. It never hurts to sprinkle a little DE around and in the nests. I add it to their dust baths, and am thinking about adding a little tobacco, just a smidge, to help with some of the pests my girls get.

The geese can be feather pullers. They are great flock guardians, so I hate to throw shade at them, but mine will get a bit "feather-pully" when they're frustrated.

The other hens will pick on her, too. And getting new feathers to grow in can be a hard thing.

My advice (which is worth what you pay for it), is to give her a safe place to run; reduce your roosters by at least one unless you really need all of them (I currently have 2 roos over 22 hens, and one will be going away soon.); put a chicken apron/saddle on her (there are several free patterns on the internet and they're easy to make - she's a medium sized hen for the purposes of the patterns); treat her skin tear with your favorite wound care (I love this blue powder that has activated carbon and sulfa powder in it. It Stops bleeding and helps the hen to heal.); and just let her heal up. It won't take too long.

Otherwise? Maybe up her protein? The other chickens will be going after any new feather growth, so watch to make sure she's not getting too harassed.
Aside from all that, she looks like a very healthy Barred Rock. Great hens.