Had 3 hybrid hens for 18months,no problems,i have just extended the hen house and added 3 point of lay hybrids to the flock.Having the usual problem introducing them but after a week they have just started going in the house together at night and the bullying as reduced dramatically.However my concern is after a couple of days 2 of the new hens started sneezing but seem otherwise ok,then 2 of my older hens started sneezing,then the next day i came home to find my goldline hen standing on her own and sneezing and rattling really bad breathing and not interested in treats. I am worried the new hens have introduced something and now all are sneezing.I have put tonic and mintamix solution in the water supposed to help respiratory disease,nugget my goldline seems alot brighter today eating and drinking and looking much better but she is still making horrible noises breathing and i can hear her sneezing in coop at night. I dont have anywhere to separate even if i wanted to but is this some kind of infectious disease or just a cold i'm not sure what to do for the best?? Any advice or experience of these symptoms?? Thanks.