A couple of mine had the pasty butt problem for the first week, and I took the advice some gave here about yogurt and hard boiled egg yolk. Not sure if they just grew out of it or if it really helped, but after a couple days of those treats, their fluffy little hienies were fine. I mixed the yougurt in with their food (a lot of food to where it is still crumbly and held it under their brooder light for a min to let it warm up). They were timid the first time or so but after that they went crazy for it. They went crazy for the egg from the beginning. Good luck!
edited for spelling