The Effect of Congenital Passive Immunity Levels on the Response of Chicks to Newcastle Disease Vaccination

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Abstract
Summary: Individual vaccination of 1-day-old chicks with a single application of the B1 strain of New-castle disease virus resulted in a serologic response inversely related to the quantity of congenital passive antibodies. A serologic “level of significance” titer for the hemagglutination inhibition (HI) or neutralization indices (NI) tests could be correlated with the resistance to challenge only in chicks with the least amount of congenital immunity during the 8-week test period. A transitory infection of 1-day-old chicks possessing increasing amounts of congenital immunity was evident in that HI and NI antibodies of the control chicks decreased more rapidly than those of the vaccinated birds. The susceptibility to challenge at weekly intervals postvaccination was proportional to the degree of congenital Newcastle disease immunity in 1-day-old chicks. Cumulative challenge mortality during the 7 to 8 weeks period was 0%, 10% and 27% among groups of vaccinated birds having increasing amounts of congenital antibodies.