This is a great discussion. I do have some questions, though. I bought some chicks last summer from someone who was NPIP-----I thought this meant their flock was reasonably healthy and vaccinated. Well, some of the chicks became ill----not respiratory (I don't think)----their eyes ended up being "stuck" shut and they basically just wasted away. There were 10 chicks, and any that developed symptoms died---leaving 5 healthy chicks. They were never around any of my flock, except for 3 chicks of about the same age that I had hatched in the house and who never developed any symptoms. I don't know if this means that whatever the new chicks got was something on my property that my chickens were resistant to or what. All the chicks were integrated into my original flock after all the sick ones had died. Now some of my chickens are showing signs of being ill-----nothing that seems serious, just some of them kind of coughing or sneezing---no drainage from eyes or nostrils or even acting ill, just these weird coughs every now and then. I did add apple cider vinegar to their water as well as an antibiotic over the weekend. Do most on here think I should cull all the birds who are sneezing or coughing? I would hate to do that as it doesn't seem serious, but don't want a "sick" flock either.
I would consider any bird coughing or sneezing a serious problem. I don't have any recommendations other than watch the flock and be sure that you don't get around other birds until you find out what is going on with your birds. Keep the sick birds away from the birds that are OK. You can try antibiotics, but be sure that you give them for the recommended amount of time. They will not help the birds if it is a virus.
It is very difficult to diagnose poultry illnesses.