I have 5 - 7 week old chicks that all hatched on the same day. They are different breeds though, with my white rock being the biggest, by far. She is also the only one that is white. Her butt is dirty all of the time and I noticed last night when I went to clean her bum - worried it was pasty - that she has limited feathers on her breast as well. The other chicks are all fully feathered out. Is this normal for her breed or age? Here are some pics of her. She is acting normal, but with it being cold especially, I want to make sure she's ok.