The objective of this work is to evaluate field situation depends on vaccinating bird from breeder flock, then mixing them with the rest of the flock to transfer vaccine virus to all birds in the flock. Two breeder flocks was vaccinated with attenuated live vaccine of CIV, all birds in the first flock was vaccinated, while only 20% of birds in the second flock was vaccinated. The samples was collected from the two breeder flocks and their progenies. Then ELISA test was applied to all samples and showed that CV% in full vaccinated breeders and their progenies was more than the others. Zero titers of antibodies was compared between the two breeder flocks and their progenies, also the percentage of titers above 5000 was compared between the two breeder flocks. Other subjects was studied in this work, and all results showed the necessity of vaccinating all birds in breeder flocks.