I have a nine month old cream legbar who is the problem du jour. I saw her go in early in the morning, and assumed it was to lay an egg. I was cleaning the coop, changing waters etc so was there to observe that my bully RIR went and took over that particular nest box-- and Agnes left and I figured no big deal. Late afternoon, I went to gather eggs and throw scratch-- and Agnes was in a different nest box. I thought it was odd that she has waited ALL DAY to return to lay her egg. Then at dark, when I went to close the door, she's still in there. I tried to gently evict her but she was adamant about staying. I'd push her out, she'd flap and flop and come back in. Eventually I just let her stay, since it was now dark and there was not a good empty spot on the roost where we would not risk being pecked.
Figured by morning's light she'd be out eating, ready for me to open the door to the pen. Wrong. She just wants to be in that box. I put her outside, she came back to the box. She was a little wobbly/unsteady. The rooster was very concerned, circling her and making little noises-- too cute. I separated her with food and water, and she just sat there. Came in to google and search broodiness, foul crop, etc etc then went back out and carefully examined her in the bright sunshine.. Empty crop, wet/dirty belly, red comb but with a little bit of ashy stuff. No mites. No sign of being egg bound. No injuries. But pretty limp/lethargic.
At this point I brought her into the house to get her away from the nesting boxes, and warm/safe. I washed her dirty spots, and towel dried. She's in the shower (with a door) on a towel. No interest in scrambled eggs, lettuce, layer pellets or crumbles. Or water.
Gave it a few hours, then put the above food in some water with electrolytes and vitamins, and ran it through a blender. Wrapped Ms Agnes in a towel, and tried to put some down her throat with a pipette. She lost her lethargy and was pretty energetic in objecting to this process. I got her to drink/swallow a tiny bit, and got quite a bit on myself and her towel. So she's spending the night, in the dark quiet shower stall, on a towel. She has fresh water and that soupy mix. She's just sitting there, in the roosting position.
She seems to be in a trance. No interest in eating. Since the weather was mild, I moved her to a small wire cage in the coop and she got a little brighter, and drank a little. But just sits there, sometimes not even quite upright. She seems exhausted.
Someone said maybe Mareks --she ate medicated chick starter til she started to lay. She's been laying for a couple, maybe three months.