My chickens recently had a mite problem and I dusted them with Sevin Dust. I dusted them twice, 10 days apart. Today I checked them over if there is still a problem since some of them look still a little bit "scruffy" and their feathers on their back/hind are still fluffed up (don't know how else to describe it). On my broody which was the easiest to inspect I found this "growth" on her back/butt. What it is?????