Antibody Response and Resistance of Turkeys to Newcastle Disease Vaccine Strain LaSota

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Abstract
Studies were undertaken to determine the influence of repeated revaccination on the immune response in immunocompetent turkeys as measured by humoral antibody and resistance to challenge. Protection was better in turkeys given the LaSota spray vaccine at 4 wk and 30 days later than in turkeys given 1 vaccination by spray or i.m. route, or exposed 4 times at 10-day intervals by the aerosol route. The anamnestic response, as measured by the hemagglutination inhibition [HI] tests to revaccination with the same immunogen, was not evident by the 3rd day postrevaccination, but was observed on the 7th day. The interval between primary and secondary vaccination was important to a true and optimal anamnestic response. Response was greater in vaccinated turkeys exposed to velogenic viscerotropic Newcastle disease, a more virulent virus antigenically different from the vaccine strain. Exposure to LaSota vaccine by i.m. route gave a poorer HI response than LaSota given by aerosol.