I have a sick RIR. She has been in a cage in the bathroom for a couple of days now and hasn't changed much. She is having trouble walking. She can half stand, but tends to stand with one foot on top of the other. When she walks she seems off balance and uses her wings to balance herself when she's laying down. She is alert and eating/drinking/pooping. Her poop is runnier today. I don't know how much she weighs or how much she did weigh. Her comb looks normal, although she has a dark smudge on it with a dark smudge on her head by the comb also. I tried to wash it and got a little off. It looks slightly greeninsh on the rag. It's hard, she doesn't like it being touched, but she never really did like being touched (unlike my other RIR.) She can move around some but seems unable to control her legs/feet very well. The other 4 hens seem fine, so far. I also have 6 16 week olds in another coop that are also OK. How can I tell if it's Marek's. She's just over 1 year old(10/09 hatch), so I wouldn't expect it, but if it is how would I know? I have been reading about diseases but it's hard to pinpoint what to look for to make the final diagnosis. She has been eating Cascade Organic soy/corn free layer mash for about 4 months. She doesn't seem to want that now unless I make it into a warm watery mash, then she eats it fine. She also is eating yogurt, but won't eat scrambled egg. The hens are housed in an open-air coop (this is the AZ desert) with deep-litter. They also free-range most of the day on my 1/2 acre lot with grass(rye at the moment, bermuda in the summer). I did cover most of the front of the coop with a shower curtain during the "cold" snap we had last week. It actually got down to the mid 20s. We (and the chickens) aren't used to that. There is a picture of my coop on my page.