I have 20 chickens, all have had perfectly fluffy butts until recently. I have one Buff Orp that has gotten a poopy butt, I just washed her off and put on some olive oil, since I read that it can help future poo from sticking. I also gave her some yogurt/garlic/oatmeal as a distraction while I was cleaning her up. Which she loved by the way and held perfectly still for all the cleaning without me holding onto her. Yay! I was expecting a wild ride since I didn't have any help. She is I think almost ready to lay, her pelvic bones are 2 fingers apart and she has been laying on the straw floor and keeping her back end pointed slightly more downward the last day or so. Maybe she is preparing for egg laying and the weirdness has caused the sudden poopy butt? No signs of lice, mites or eggs. I will keep an eye on her, a couple more days of cleaning and yogurt oatmeal if necessary, then a trim if that doesn't work.