We have 7 apparently healthy chickens. One chicken however has a very sore looking, red and featherless backside. It's been like that for quite a while. I bathed her bottom yesterday and it looks to me as though she has diarrhea which has scalded her skin. Any ideas ... To date, i have not done any parasite or pest control. To be honest, I was not aware that was something i had to do. Please - any advise would be so welcome.