Pasty butt is a condition in chickens where some of their feces becomes stuck and clogs their cloacas. This is a life threatening issue if not resolved quickly.
I just noticed that one of our new ladies may have pasty butt. I took a Q-tip and warm
water and tried to clean it. It looks like the vent is clean, but I
cannot get the dried feces off of her . After cleaning her with a Q-Tip,
I rubbed some olive oil on it to try to soften the poop.
After some searching on Backyard Chickens and Facebook chicken forums and a quick soak in warm water, she's now OK.
If you encounter this issue with your chickens, make sure that you thoroughly dry them off before returning them to their flock. If not, they will get picked on by the others.