Quote:
Just realized that this is a very old thread from 2008, but the info is still valid. Yes, the survivors would have been carriers if they did have CRD and were symptomatic. Real chicken breeders never treat illness like this. They cull for it immediately. Antibiotics don't do anything for viruses, same as with people, though I believe that CRD is bacterial. And antibiotics given to a sick bird who later recovers won't change the carrier status of that bird.
If they never showed symptoms, they probably are not carriers. You can be exposed and not catch something, or you'd get sick with every illness of every person in your doctor's waiting room, right?