Hi, ColtsRox
Sorry to hear about your sick rooster.
I know how worried you feel since I just went through the same thing. (You mentioned my post, which I have just updated, btw.)
Egg4Sale let me know about your situation, and asked if I would visit this board to see if I could offer any additional advice. It does sound very similar to what our Cobalt went through except he never lost any feathers, luckily. He did seem to lose some weight, though, since I think his breast bone became more pronounced. That's what began to worry me the most! The lack of oyster shell wouldn't have anything to do with it, since I've never even given it to my chickens. Our hens seem to lay eggs just fine, and I just never got around to adding it yet. I don't see how it could affect your rooster's health, either way.
First off, Cobalt seemed to act tired and lethargic and eventually lost his appetite. His wattle and comb appeared to get paler or duller than usual. Basically, he looked kinda depressed... he walked really slowly and let his tail droop down. Those were the signs that let me know something was wrong. I never saw any blood in the stools, or diarrhea. In fact, in the beginning, his poop was quite firm. Later on, though, it did become watery because he wasn't eating enough.
I suggest you do all the things I did, since something (or the combination) seemed to do the trick. The first thing I did was put him in a cage in the house. This separated him from the flock, to prevent the spread of possible illness, to prevent him from getting bullied or picked on, and to eliminate any stress caused by heat. I also added VetRx for poultry to his water, and made sure he drank by offering it to him whenever I could. (I kept dripping some onto his beak, or dipping his beak into the water until he cooperated.)
When I didn't notice any respiratory distress, I figured that the VetRx wasn't really the right medication for these symptoms. That's when I decided to add Duramycin-10 to the water instead. You can use another similar broad-spectrum antiobiotic powder, such as Aureomcyin or Tetramycin, found at most livestock feed stores. As others mentioned to me, you should always use antiobiotics for the full 7 days once you start it, or you could inadvertently create a "super-bug" that is resistant to treatment. During all this, I also wondered about lice or mites, so I sprayed all the chickens with Poultry Protection and thoroughly cleaned the coop. I never saw any signs of infestation, but it couldn't hurt to cover everything.
I still didn't see much improvement in Cobalt right away, and started to worry about his lack of energy and loss of appetite. I began to think that he was continuing to decline due to lack of nutrition. That's when I realized he needed some sort of vitamin supplement or electrolytes. I asked around on this board and at the livestock store, and I decided to use Nutri-drench which can be given as an oral treatment and added to the water supply. I opted for the "Rapid Recovery" dosage, which I administered directly into his beak every few hours. I was desperate to keep his strength up, because he seemed to sleep all the time.
The best advice I can give is to start forcing him to eat! I think the lack of appetite is what would finish him off the quickest. I started hard-boiling eggs and offering him the crushed up yolks. At first, he did seem slightly interested but not enough to make him eat well. I also offered him some yogurt crumbles mash, but he only ate what I could stick to his beak while he stood there. Finally, I made him fill his crop by opening his beak with my fingers and dropping the egg yolk into his beak until I could feel a small bulge from his crop. The very next morning after his first forced-feeding, I could see an improvement in the consistency of his poop. I think he also had more vigor, but he still needed one or two more TLC feedings. I might have hand-fed him for longer, but I had to leave for vacation.
The next feeding I gave included Layena crumbles, which is what he was used to getting. Be sure he is drinking enough, as well. I made sure by using an eye dropper to pour medicated water into his beak after each feeding. When he started acting a bit better, I started offering him other pet foods to see if I could stimulate his taste buds, such as cat and rabbit food. He acted interested in picking out the cracked corn from the rabbit feed, so I ran right out and bought both Layena pellets and cracked corn, to offer all the chickens a variety. It must have worked, 'cause he started pecking at it and eventually he started eating and drinking regularly again.
I hope some of my techniques can help you and your roo. I really think the Nutri-drench and the egg yolk forced-feedings were critical in keeping his strength up while he recovered from whatever illness he was suffering from. I recommend you start that as soon as possible, and medicate as you feel necessary. My hens and the other rooster never got sick at all, so hopefully you'll just have to concentrate your energies on this one rooster.
Good luck and be sure to keep us posted on your ordeal. I'll keep checking to see if you have any questions I can help with.