I have a hen that seems to have a lot of poop stuck to her backside and also under her wings it seems he has no feathers. Last week I added DE to their dust baths to see if that would help with any type of mite/lice issue (tho' I have not seen evidence of any). And I put a cap full of Braggs Raw Apple Cider Vinegar to each gallon of water that they have. We have four hens and one rooster and she seems to be the oldest hen. Not sure what is causing the featherless area under her wings. I have only had these hens for about 7 months and all seems to be going fine until recently. Any Ideas?