I have 16 Red Sex Link hens that are 24wks old. I noticed one of them this afternoon had a congested sound when breathing. No nasal discharge, watery eyes, or any other symptoms. I isolated her and picked up some Oxytetracycline powder. My question is do I have to treat the entire flock since no one else has any symptoms? Can I just treat this one hen and if any others get any symptoms then treat the entire flock? Any advice would be greatly appreciated.