It's been really cold the last few weeks and even though they sleep in a heated and insulated coop, I'm worried about during the day when they are free ranging. Some of my hens are losing feathers on their backs right before where their tail feathers start. I'm not sure if this is from my roosters mating them, (the roosters have been mating for months now and this is the first time I've seen the hens losing feathers) The hens are around 10-12 months old. I would like some help on this topic to see if this is alright.
Check them for external parasites. Look on the feathers and skin near the vent, under the wings, and beneath the neck feathers for moving black specks (mites) or yellow blobs (lice). If you see any, treat by dusting with 5% Sevin dust, poultry dust, or by spraying with another mite/lice spray. Clean out the coop and spray it with vinegar, liquid Sevin, or a mite/lice spray. This should get rid of the mites, though you should redust/spray the birds 7-10 days later to kill any hatched eggs.
Its also possible that your birds are molting. That is common in 1 to 1 1/2 year old chickens, especially as the days get shorter and cooler. If this is the case, you should see some feathers in their quill form growing in the bare areas. Most birds molt without help, but if you think they're having trouble, try increasing their protein intake. Feed a higher protein feed, like chick starter or game bird, see if they like cat food or scrambled eggs, or give them a handful of black oil sunflower seeds daily.
The only other possibility that I can think of right now is that the feathers are being ripped out by a rooster, or another aggressive hen. Some hens seem to be more prone to overmating; you may want to get a special "hen apron" to put on the more badly de-feathered birds. If possible, isolate the rooster(s) and see if the feathers grow back in.
