I have a very sick chick. She is about 16 wks old. We found her this morning with a bloody abscess coming out of her. I have been researching this disease and after a run to the local farm store to get Corid and mix in her water. I was able to inspect her bum. It looks like it could be intestines that is coming out of her. She is lethargic and feathers are disheveled. I could not get her to drink out of my syringe.
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Photos might help.
From what you are describing it sounds like a prolapsed vent. You will want to separate her.
Bring her in give her a soak in a warm bath of epsom salts. Clean up the prolapse with some vetericyn, diluted betadine or something similar (it will most likely have poop on the prolapse). Gently try to push it back in you can apply some Hemorrhoid cream or honey to help reduce the swelling, you may have to repeat. Sometimes some calcium will help with the contraction of the oviduct, you can crush a Tums and give to her if you want.
Keep her isolated so you can monitor her for a while to see if the prolapse stays in. Make sure she drinks and eats.
More detailed instructions are in the link below.