An evaluation of Newcastle disease virus spray vaccination programs of market turkeys

Commercial market turkeys that were spray-vaccinated at 2 to 3 weeks of age with viable Newcastle disease virus (NDV) vaccine usually did not develop high or persistent levels of serum antibody as detected by the hemagglutination-inhibition test. Vaccinated turkeys exhibited a satisfactory level of resistance to infection and clinical disease when challenged by the oculonasal or aerosol route at 2 weeks post-vaccination, and they resisted clinical disease when challenged at 6 weeks, but the level of protection diminished by 10 weeks post-vaccination. It is suggested that market turkeys produced in an NDV-enzootic area may require two or more NDV vaccinations by spray during their growing period in order to be adequately protected against natural NDV infection.