Well, the red hen that was lethargic/depressed died overnight. I still have no idea what was wrong with her. The onset of her illness was about 2 weeks ago, a few days into which I started treating the entire flock for coccidiosis. She was perking up after about 5-6 days and then nosedived the last 24-36 hours. No one else is showing any of the same listlessness or inactivity she was. I checked her over a couple days ago pretty thoroughly for mites/lice/anything else I could observe on her, nothing.
I’ve pulled the corn, so they just have the Poulin crumble right now. I’ll continue to do some research into feeds and see if I can’t get them switched to something with more protein and not so heavily corn-based.