If not treated, pasty butt can kill them. Chicks with pasty butt often also have coccidiosis.
-Kathy
So what can I do to make sure these other chicks don't die?
Keep their butts clean, keep their brooder warm, dry and clean, feed them fresh chick crumbles and fresh water. Might also be a good idea to buy some Corid, Amprol or AmproMed in case they start to look sick.
-Kathy