Pasty butt indicates GI troubles, often as a result of stress, chilling or feeding soybased feed too soon.
Shipped chicks are prone to it, most folks saying its the result of chilling during transit.
Prevention is the real key - once they have it, it's too late. Chicks have enough to deal with in the first days of life that they dont need GI complications, too. Mother hens know this, I guess. They take the chicks around the first few days and they pick a little at this and that, but they feed sparingly. So, I rarely give them anything but chopped oatmeal, hardboiled egg and a little crushed CalfManna for the first 2 days after their intitial 72 hours. This and water is it.
Just put a little of any of these in with them and watch. They only pick and sort of mess with it at first, with no real gusto to their efforts. When they get over their birth stress, it soon becomes apparent when they are hungry enough for real feed!
I deal with pasty butt a little more bluntly than most, too, I guess. I fill a bowl with warm water and just dunk their little heinies in it. Hold them there for a few seconds as the poo softens and then work at it gently until it comes off... aint chickens great?
Once you clear the plug, just dry them off well and get them back in the warm brooder.
A good book on how to manage chicks is "Success with Baby Chicks," by Bob Plamondon. Just google it, or look for it on any of the online bookmongers.