Chicken has black butt

[T71446]

I went out today to wash the back end of one of older layers. She no longer lays and smears. After washing her off noticed that her skin was Black and looked bad. Posted a picture. Hopefully someone knows what this is and can give some advise. Never seen anything like this before and google has no answers.

 

[Eggcessive]

Welcome to BYC. It looks like she may have been injured by pecking. Frequently there can be maggot infestation in the wound, and that is called flystrike. I would bring in and soak her bottom in a dish pan with warm Epsom salts water, or water with btpetadine, chlorhexidene, or dish soap. Let her site for 20 minutes or so, and look for any evepidence of live maggots. If you do pick as many off with tweezers. If no maggots, dry her off, and apply plain Neosporin or Triple Antibiotic Ointment to her bottom. Keep her isolated from other chickens and away from any flies. Let us know what you find. Many times a hen will be bullied or pecked by other chickens. If one sees red skin, they all may join in.

 

[Eggcessive]

Here are a couple of good links to read if it turns out to be flystrike:
https://the-chicken-chick.com/flystrike-in-backyard-chickens-causes/

https://www.backyardchickens.com/th...y-tale-with-graphic-photo-progression.712322/