Ihave a black copper maran pullet that I bought a little over a week ago, when I got it home I noticed she has a cough. I have been treating her with tylan for 6-7 days and no improvement. She is coughing occasionally and when stressed she has gurgling breathing. She sounds like we do if we have upper respiratory infection. I can't cull her. She is eating fine and has no other symptoms. Any suggestions?