hey,im trying to figure out what is wrong with our chickens..we have six black stars for a year now.. after like eight months they lost all butt feathers but were laying eggs. We bought ten more chickens that are full grown and they all looked healthy but in the past month they have lost their butt feathers also. So all my chickens have bare butts but are laying and acting healthy..I have dusted their pens and have dusted all the chickens..no change I moved their pens to another part of the yard and dusted the area before moving and after again and no change..I cant find any bugs..I changed to shavingsevery two weeks and no improvement..I have been adding black oil sunflower seeds and have been feeding the scratch and nothing..any ideas i have ran out of ideas.