I don't know, they've never been sick before.
And I've added chicks several times.
The new birds were in a separate pen and the new birds had symptoms almost a week before the originals in the pen with the older ones.
I'm almost positive it came from the red sex links from the auction.
I've had a lot of stressful incidents with other animals, and dogs getting into my pen on multiple occassions and killing two. And no one ever got sick until these new ones came to the property.
Anyway, I've got a question on adding new chicks. Not doing anything now, but probably this Fall when everything calms down from summer I'm letting my kids each get a barred rock chick to replace the ones they lost and my husband wants a RIR. How does this work with the other birds. As long as they are healthy at the time, the chicks won't get sick? Then if for some reason the adults do get sick, the chicks will as well?