One of my beautiful chickens has developed this sort of cough or sneeze. I dont see any liquid coming from her nose or eyes and her crop is still nice and red. I bought some tetracycline to put in her water but I dont know if I should treat all my girls or just her. None of my other chickens show any sign of distress or cough/sneeze and they are all active and hungry. Thanks in advance for any advice. It is very welcome to all of us new chicks!