Featherless butt with some blood

[Meni120]

I noticed this big bare patch on her butt this evening when closing the coop. She was normal yesterday and laid a huge egg today. She’s about 30 weeks old. I did just introduce three new 14 week olds after 4 weeks of see-but-no-touch integration.

 

[dawg53]

Please see post #2 in this link for treatment:
https://www.backyardchickens.com/threads/bare-rooster-neck.1557282/