I have tried just about everything to prevent my chickens from getting sick. In August I lost 4 birds to Infectious Bronchitis. All of which were immediately removed from the coop when they started showing symptoms. No other birds were infected. In early October I purchased 7 new juveniles to put in their own pen away from my older girls and roosters. a partridge silkie, black silkie, jubilee orpington, lavender orpington, buff laced polish, belgium d'uncle, and a silver laced wyandotte. The belgium d'uncle was picked up by what we believe was a hawk. However, a week after settling them in I noticed my black silkie, Oprah, was sneezing uncontrollably and her nose was running everywhere. As soon as I realized this I removed her and put her inside our camper in a rabbit cage. I began administering injectable Tylan 200 twice a day. She was not getting better. So I took her to the vet and he gave me another liquid medicine. She's not any better but she is still very active and has a huge appetite. I refuse to give up on this little girl. Her nose constantly runs to the point where is dries up and I have to peel dried mucous off her nostril. Her eye is also shut because it is also running. I'm not sure what else to do for her. Now it is November and I realized today my Jubilee Orpington has a runny nose! I am confident that he did not catch it from Oprah since she has been secluded in the camper for so long and I have been very cautious about bio security. Does anyone have any idea how my Jubilee could have gotten sick? Or could her runny nose simply be from the weather? I'm from Lancaster Pennsylvania and it's been very cold here for the past few weeks. I'm not sure how to prevent this illness from popping up over and over. It seems like every time I catch a break another pops up with symptoms!
How much ventilation do the building have in sq. ft. of openings in each building and how much sq. footage of floor space? IB has no cure and can travel long distances in the air, probably farther than your distance between coops. Clearly your birds have something other than a bacterial issue that is susceptible to antibiotics. If you don't want to give up on her, you'll need a good avian vet with poultry experience to do loads of lab work. That can be pricey and may determine the problem has no cure. A better course is to take one of the birds with the same symptoms to the state poultry lab (usually a vet school) to be humanely euthanized and necropsied. Then you'll know for sure what the problem is and it's much cheaper and more conclusive than lab work on a live bird. Any other course of action can be prolonging any solution.
Our larger coop for the hens has great ventilation. It is a little bigger than a large shed and has a run attached to it which is the same size as the coop itself. The girls stay out all day in a huge fenced in area and only return to the coop to sleep. It has a ventilation system we put in right below the roof of the coop on opposite sides. Just enough for ventilation, but not drafty. As of now I do not have any birds in this coop sick. My juveniles are in a small coop that I purchased from tractor supply which holds about 4-6 birds. I didn't want to get anything bigger since they will only be in this until they are big enough to go in with the hens. They also have a large fenced in area around the coop that is probably about 20ft x 20ft. They also stay out all day free ranging. I keep the juveniles sleeping area filled with straw so they do not get cold and I have a very safe set up for a heat lamp for extremely cold nights. I will admit, the juveniles are not in a coop with very good ventilation. I was hoping to have them in with the big girls by this time but my polish and silkie are still very small and I'm scared the big girls will hurt them. The juvies are all between 16-17 weeks and the 6 older girls are anywhere from 24-30 weeks. Only two of them started laying. My next door neighbors along with the people living behind me, both are acres away, have recently gotten chickens. I'm worried they may not be taking care of their birds the way I do and diseases they are infected with are being carried to my birds. If that's the case I can't force them to take care of their birds better to prevent illness. I took the 4 birds that I lost in August for Necropsies. All of which came back with them having IB that went "tubular". From what I gathered that means it became so bad that they had what looked like tumors filling their lungs. They were clear for everything else. My Silkie that is currently sick does not seem to have the same symptoms. She's not wheezing or breathing heavy. The vet said her lungs sounded fairly clear. Her illness is all in her right nostril and eye. She was taken to poultry vet. She had a fecal sample done and it came back clear. He diagnosed her with IB. She hasn't gotten any worse, but she hasn't gotten better either since antibiotics which makes me think it would have to be viral.
Infectious Bronchitis IS a virus in which antibiotics are ineffective. There is a vaccine for IB. It can be given to your non infected birds. Here's info about the IB vaccine or you can look for more info online. http://www.infectious-bronchitis.com/vaccination-programs.asp