Chickens in good condition molt twice a year, in the spring they shed all of their winter under down that keeps them warm in the winter, the fine fluffy stuff you never see unless your doing a good inspection of a bird for some reason. They molt again in the fall, this molt sheds the bigger main feathers and also the hen will again begin to grow her soft fluffy under down in preperation for the cold. Hen's rarely molt on their backs and when they do molt it is never a full blown lose all the feather type molt many newby's would have you believe, a chicken just isn't wired that way. They shed feathers at different places on their bodies at different times so as not to leave them bare, the chest and underbelly is first, followed by the rear end and some neck and hackle feathers. If your hens are bare backed it is almost allways from the rooster being too vigirous, or from mites and lice. During the height of the spring laying season they are knee deep in laying and laying heavy, this will stress them a tad and may lack additional protein to keep feathers in top shape. Most folks don't consider this and think a normal run of the mill layer ration is enough and it may be for some hen's but for some they need a top dressed feed bucket twice a week and this will help.
Molts only last 6-7 weeks and if your birds health is good and their diet is as it should be you will never see a molt, all you will see is a butt load of faethers in the coops, yard, run's, nest boxes and such this is normal. near the end of a molt be sure to add some extra protien to their diet to help the feathers come in real nice, I am not a fan of the whole cat food protein thing, cat food is for cat's, and most people do this cause it's just lying around anyway and their to cheap to buy a bag of seperate high pro chicken feed. feed them a small bag of a better ration for a week or so and then your fine.
Your rooster ratio is fine it's just your roosters are being rough just to show the other roo that he's got it goin on more than the other roo, that's it. And that is what makes their backs bare. I have never had a molting chicken look bare or otherwise unthrifty looking due to a molt. Now WTS and I know many will discard this bit of advice but many many hatchery type stock will have poor skin and feather quality due to their mix breeding and god knows what else they lack, and this will contribute to a god awfull looking bird at times, what did you expect from $1.50 chick. So there it is in a nutshell.
