Overbreeding

You worded it fine.
They're his favorites. You could get more hens or put a saddle on them temporarily.

 

How old are they? I’m guessing they are still relatively young.

There are a few different things that might be going on. It’s possible these two are the rooster’s favorites and he is overbreeding them. But I doubt that is all there is to it. By the way, losing an occasional feather during the mating process is normal. It’s when enough come off to bare skin that it becomes a problem.

A lot of times young roosters don’t have the greatest technique. They haven’t figured out how to go through the mating ritual correctly. The pullets need to do their part too and not resist too much, but it’s quite possible the rooster is grabbing onto the feathers with his claws and causing damage. Most of the time they get better with maturity but it does put your pullets at risk until that young rooster and the pullets mature enough to get it right.. If enough feathers come off and bare the skin, he might cut them with his claws. Often the other chickens will peck at open bloody sores. That can kill the hen.

If this is the case, what I suggest is trimming the toenails. Those toenails are like yours in that they have a quick that will bleed if you cut it but you can cut off the sharp point of those toenails and blunt them without hurting him at all. I use a Dremel tool and that disc you use to cut metal. Just wrap his wings in a towel to keep him under control. Some people will tell you that he is cutting them with his spurs, but a young rooster may not have much of a spur when this is going on. The spur he does have is a lot like the toenails. It has a quick, but you can cut off about 1/3 of the spur to blunt the point without hurting him. Have some flour handy to throw on to stop the bleeding if you get too deep, but even if you do get too deep, he’ll heal up fine. Try to avoid it but it’s not the end of the world if you nick him a bit.

Another possibility that I’ve had, those two might have brittle feathers. The feathers jus break really easily. Through no fault of the rooster, the feathers just break. To be pretty blunt about it, when that hen went into the cock pot, all my barebacked hen problems went away. Brittle feathers are hereditary. I was not going to let that hen breed and pass those genes on into my flock.

When you are having this kind of problem it’s never a bad idea to check them for mites and lice. It’s not likely that is the sole cause of this problem if the feather loss is on the small of their back, but it’s still good practice to check. It’s quite possible it’s a combination of some of these.

If those feathers broke off, they will not come back until the hen molts. If the entire shaft came out that feather should grow back in the next month or two.

Those chicken saddles can help solve the problem.

Chicken Saddle Patterns
https://www.backyardchickens.com/forum/viewtopic.php?id=407575

Good luck. This kind of problem is too common.