I have noticed some stuff going on with them and I didn't know what it was till I read a thread earlier of which had the same problem I was having any way what should i be giving them because I know they need vitamins if this is happening!
Feather eating can be a sign that they aren't getting enough protein. How old are your chickens and what are you feeding them. A good layer of 16% protein is adequate most of the time but they need more if they are feathering out after molting.
Vitamins aren't necessary if your birds are fed a proper chicken feed.
Are they bored? Do they have adequate room to roam? Do they have access to greens and things to amuse themselves with, like broccoli or cauliflower hung on a line for them to peck at? Do they need some calcium?
Sometimes chickens will eat feathers out of sheer boredom. Also chickens can start picking feathers off of each other in a form of cannibalism if they don't have enough room in their pen. The minimums recommended in the coop thread are just minimums. Most chickens do better with more room.
You might try to give them some protein booster. Young hens like yours are probably laying all winter and could use a bit of help. A handful of good high protein dry cat food once and a while is good as is the occasional scrambled egg. I give mine a bit of raw hamburger once every couple of weeks in the winter.
You could put some electrolytes and vitamin additives in their water to help with some Vitamin D which can be a problem in the winter. Just make sure you read the dilution directions carefully.
I agree with fiberart 57. Purchase gamebird feed for them to eat. It has higher protein content, about 22%+ vs regular 16-18% layer feed. Then wean them off the gamebird bird feed when the sack is nearly empty and mix it with the layer feed til gone.
I heard that you can give your chickens Vitamin C to help with mosquito's and also keep them hydrated in the Summertime heat...... I was told by a friend that you can use (1) 500mg tablet of over the counter vitamin c at your local store (ie walmart) and place the tablet in the chickens water containers..... I don't know how much of this is true, but I am always willing to try a remedy atleast once to see if it works.....