I’m not sure if you mean pasty butt. Soo I’ll tell you what that is first in case that’s what you mean. Pasty butt is when poo gets stuck to a chicks down that surrounds their vent. This causes all the poo to pile up on top of itself eventually blocking the vent. The chick, or chicken, is then unable to poop. I’ve only ever heard of it as a big problem in chicks but I think chickens can get it too. Although poo just stuck to a chickens feathers is not pasty butt. Since their vent is not blocked.
Then I found this link on poopy butt. It’s the only link I was actually able to find. Besides stuff on vent gleet which is something totally different.
https://www.raising-chickens.org/poopy-butt-.html
This website is old so I don’t know how relevant the information still is.