[Serological response and resistance to Newcastle disease in vaccinated poultry]

Studies was the titer of antihemagglutinins of a total of 3263 serum samples taken from birds routinely vaccinated against Newcastle disease, originating from various poultry farms of the country. Chosen were 139 birds in which a weak serologic response was established through spray, aerosol, and injectable live vaccines (strain La Sota, Komarov). These birds were challenged by intramuscular application of 10(6) ELD50/bird of a velogenic viscerotropic virus of ND. High specific resistance was established in the various groups of birds regardless of the low level of serum antihemagglutinins. In all such cases individual birds of the flock responded after vaccination with a high titer of serum antibodies, so the application of an active vaccine was indicated.