Laboratory evaluation of live and inactivated Newcastle disease vaccines: Their application in the Newcastle disease enzootic region

Laboratory trial was conducted to evaluate the efficacy of live and inactivated Newcastle disease (ND) virus vaccines using SPF birds and broilers. The speed of protection administrated by each spray and eye drop vaccination was evaluated. The serological and post-challenge data indicated that most respiratory and enteric strains of ND live vaccines used in this study induced solid antibody responses as well as early protection against challenge by either fine spray or eye drop vaccination. Furthermore, we did not found significant post vaccination reactions caused by fine spray vaccination if properly administered. However, most enteric strains of ND live vaccine, except the VG/GA strain, did not induce both solid serological reactions and not provide early protection against challenge by coarse spray vaccination, and needed about 10 times higher virus titers compared to the respiratory strains of ND live vaccine for early protection. Present studies also elucidated that simultaneous vaccinations with live vaccine by fine spray and inactivated oil vaccine, were useful methods for broilers in ND enzootic season. These data indicated that the type of vaccine strain, vaccination method, vaccine dose, and the particle size of sprayer influenced the efficacy of ND vaccine.