Familial differences in antibody response of broiler chickens to vaccination with attenuated and inactivated Newcastle disease virus vaccine.

Genetic differences in immune response to Newcastle disease virus (NDV) were studied in 4-week-old broilers, vaccinated with attenuated (live) or inactivated NDV. The experiment included 370 chicks from two farms distributed among 22 sire families and 60 dam families. Results in chicks from both farms were similar. Survival after challenge was closely related to titer level. The genetic correlation between day-7 and day-12 titers (attenuated virus) was 1.0. Significant differences were found between sire families in both sorts of vaccinations. Heritabilities based on the sire variance components for attenuated and inactivated virus vaccinations were respectively 0.31 and 0.60. The genetic correlation between them was 0.49. Nevertheless, it is concluded that selection for response to NDV based on inactivated virus may be most effective in improving response to attenuated NDV vaccinations.