my flock had a couple girls that started sneezing/coughing. I treated the flock with tetracycline and I just found one of my Roos dead. All of them are now sneezing. What is causing this??? I have not introduced any new birds, not visited any other poultry! I have another coop with guineas, 3 chicks and 78 meat birds but no sickness found with any of them. Any help and tips so I don't lose my other flock!?!? Greatly appreciated!