My gut is telling me it is CRD. We have dealt with it before. When a flock is healthy you see it very rarely. We treat adult birds with Tylan 50 and young chicks with LS 50. Should I just let the illness run its course with little intervention and observe the quarantined group or are they even worth dealing with?
When if ever will I know it is safe to introduce them to my other chickens if it is only CRD?
How will I know if it is something more serious?
Sorry for all the questions..
MG is part of CRD. It leaves every infected bird a carrier permanently. You can never safely introduce any birds if they've had CRD/MG/MS. Antibiotics do not change their carrier status.