Preventing potential infection in current flock after having a sick bird on the property.

Hi there,

I recently bought 2 White Leghorn chicks at 2 weeks of age.
They were in a quarantine enclosure since I brought them home two days ago.

While one chick seemed in all respects healthy, the other begun sneezing after each sip of water and around about once a minute if she wasn't drinking.
Her throat also expanded and deflating as she breathed, and sometimes she produced a raspy sound when exhaling.

Other then those syptoms (which are distressing I know)
the sick chick seemed ok, ie. still eating, drinking, and frolicking etc.

I contacted the place where I bought the chicks from enquiring about a refund, and they have agreed to take them both back.

The chicks were exposed to my flock through air when the back door was left open, but my older birds were 40 or so meters away when this occurred. Otherwise, they had no other contact with my existing flock.

My question is, what preventative medication can I administer to my entire healthy flock (touch wood) to avoid an outbreak of something contagious?
My current breeders are a breed that are quite prone to developing respiratory illnesses (Croad Langshans), so I really want to be safe rather than sorry!

Your advice would be highly appreciated.


Nic.