Four weeks old speci fie pathogen free chicken were immuned with infectious bursal disease living vaccine. Serum neutralization ( SN ) antibody was produced 1 week after
vaccination, the peak of SN antibody titer was 161 at the third week and it still remain-ed 24 at six week after vaccination. Chickens with maternal antibody titer above 8, were vaccinated, the maternal antibody titer dropped quickly and there were no active immune re-sponse afterward.
Three week old chickens had matermal antibody above 64 from µarent could survive challenge by virulent infectious bursa! disease virus. Therefore, passive imnunization of mother hen is an ideal immune program for broider.