Since it sounds like you may have potential pasty butt in multiple chicks, check the temperatures in your brooder. Higher temps may correlate to increased instances of pasty butt. If using a heat lamp, for 1-week-olds I'd want the hotter area to be around 85-90F, with cooler areas 10F or more lower to escape to. If using a heat plate/pad, then just make sure the pad or plate isn't too hot to the touch, and that there's still cooler areas away from the heat source for them to cool off in.
