Feeding for good feather quality starts with the proper conditioning of the skin coat, proper fat content is so very important. Chickens will hardly get fat in the same sense as we humans view it, so top dress your feed daily with rendered or liquid fat's that keep/store well in the barn or coop during the different seasons. The best I have found for this is common processed lard from the store, it's inexpensive and you can buy enough to treat a decent sized flock for a full season for $10.00 or so, and it won't spoil ever. I also feed seed grains such as white and red milo which is has a heavy/healthy concentration of benificial oils, as does BOSS ( black oil sunflower seed ). high quality wild bird seed includes these seed grains in proper %.
I will often buy these seeds seperately available at any farmers coops or good feed & seed stores. then I will keep them in seperate bins in the breeder barn and custom mix them accordingly in each feeder as needed. I will mix them with a combination of high quality breeder feed, some 16% common layer feed, some added calcium if needed, then finish it off with a drizzle of softened lard or corn oil and mix.
Their skin will become softer and have a better oil transfer to feathers and also help the oil gland produce this very important byproduct. when a chicken preans itself it is spreading the oil from that gland onto it's feathers to maintain their feathers look and placement and dextarity. never apply anything directly to the feather as this will really screw them up and make the feathers sticky and attract dust & dirt which clumps and is a mess. Now as a breeder of rare LF Cornish I keep a miriad of different feed mixing aids at my disposal that is not to say you even need any of that for your birds, just take away from that what you will. Also you may think it's hard to do and sounds like allot of work, but it's not and if keeping your birds in good health is too much work.............. get another hobby LOL.
This feed mix has other beneifts as well, clearer eyes, healthier colored and textured combs and wattles, better looking feet and legs in color and feel. shiney strong beaks etc etc.