Thanks ladies. ..and actually I did read through the chicken chick links weeks ago. I still see no lice, and my hens are fine. His comb is fine as well, and no weight loss. Thankfully, he made it thru the night and even crowed this morning! Still trying to figure out which meds to give him, and why he was so lethargic yesterday. He barely moved all day long, and wouldn't even go in with the girls at dusk, ..just lay there in the grass until I went out to get him. A friend thinks he should be treated for cocci, yet he has no bad diarrhea, and no blood in it. I'm also told that worms would cause a pale comb, but does it ALWAYS? I just don't know which to treat him for. I'm going to repost this elsewhere, list his symptoms, and hope someone can help without pics of this skin issue on his rear. I can't even find an online pic that looks similar. ..and as I said, I'm not sure that these two issues are even related. Anyway, thanks again for your help. I'm just so happy he's still alive! He's not back to normal, but so far, he seems much better than he was yesterday.
I'm glad he is a bit better this morning. I didn't respond before because what you describe was just too vague. It could be anything, really.
If parasites were so bad that he was too sick to go into the coop at night, he would have some other symptoms you could see. For internal parasites, there would be stool changes. You whould see an infestation of external parasites if they are so bad that he can't get himself to bed. You certainly don't want to be stressing a bird that is as sick as he is with worming medicines, which are basically poisons.
I wonder if he has been injured somehow. Maybe a hawk or a dog attack you didn't see? Is that possible? Did he attack someone in your household who retaliated and kicked him but didn't tell you?
I believe it was you that mentioned that he was snuggled up beside your cat on a bale of hay. Lots of people don't know this, but cats carry a couple of really nasty bacteria in their saliva (and their claws) that are particularly dangerous to birds. This bacteria is so deadly to birds, that the tiniest scratch (I've read even just the saliva) can kill a bird. That is always a possibility.
A few weeks ago I found a 3.5 month old cockerel trampled in a corner of the grow out pen. I thought he was dead. He wasn't. I brought him in the house and noticed he had yellow/green urates (the white part of the poop). That color indicates a lot of things, especially liver problems. The bird was unable to stand up. I thought there were neurological problems. Not sure if the bird was sick or perhaps had eaten something toxic, maybe a mycotoxin in the organic feed he was eating. I supported him by using a tube to get fluids and electrolytes directly into his crop. I put him in a hospital cage and expected to wake up to a dead bird. He didn't die and was sitting up fairly alert the next morning, but still was not able to stand or walk. This looked more neurological than just weakness. I continued the supportive therapy of tubing fluids into him and offered him food. He got better and better each day. By about the third or fourth day, I put him in a cage outside on the grass with food and water in within easy reach since he still couldn't walk. He continued to improve and after a week or ten days, I banded him and put him back in the grow out pen. He seems quite normal now but if I follow him and he hustles out of my way, I get the impression he isn't moving as coordinated as he should, but that could just be gangly teenage klutziness going on.
I didn't post to you earlier because I would have just recommended you support him by giving him fluids, which is the standard treatment for any animal in crisis. Giving fluids to a bird who is not as easy as it sounds because the entrance to their trachea is at the back of their throat at the base of the tongue. They don't have an epiglottis (a flap that covers the windpipe when swallowing) the way mammals do. It is quite easy for a bird to aspirate fluids and drown either immediately (or later from secondary drowning) or develop aspiration pneumonia. I was taught by a vet how to tube a chicken, and I had the equipment on hand so for me it was easy to give supportive fluids. I didn't want to advise you to give him electrolytes and then have you drown the bird.
I have had some young chickens attacked by dogs and be shocky for a couple of days and then recover just fine. If he has been injured, you do not want to offer him food until he comes out of his shock. Their gastrointestinal tract shuts down when they go into shock and you will cause more problems by adding food to a GI tract that isn't working.
Good luck.