| Antibody response of broiler breeder flocks vaccinated with Avian Influenza (AI) vaccine A and B respectively were detected. The hemagglutination-inhibition (HI) antibody titer against H9 subtype was similar, whereas the geometric mean HI (GM-HI) titer to H5 subtype of A flock was 1.5-2.51og2 higher than that of B flock. There was significant difference between two flock by Student test (p<0.01)Vaccination program of AI in broiler breeders was compared. The levels of antibody in broiler breeder flocks were high at the point of lay if they received three vaccinations before. The breeders had the GM-HI titer to H9 subtype higher than 7 log2 and that to H5 subtype was higher than 51og2. As a result of 2-3 repeated vaccination at the interval of 12-16 weeks, the high level of antibody response could be maintained in the breeders during laying period.The maternal antibody in chicks were proportionally related with the levels of antibody present in the dams at the time of the eggs were laid. The GM-HI antibody liters of breeders was 2-31og2 higher than those of chicks. The maternal antibody decreased to a very low level at the age of 28 day. It decreased most rapidly at the age of 7-14 days. Vaccination at the age of 7-10 days could get a good immune efficacy.Broilers with the antibody levels to H5 subtype of 4-61og2 could survive from the challenge with the same type of virus, but some lesions could be found. These broilers had an antibody titer increase of 2-3 log2 post infection.
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