Immune responsiveness to IBDV vaccine in SDL broiler chicken lines divergently selected for immunocompetence index

Birds having extreme immunocompetence (IC) index in G₂ generation of divergent selection based on IC-index were evaluated for immunoresponsiveness to IBDV vaccine. The lines differed significantly (P<0.01) in antibody response to IBDV vaccine at 14 dpi. Peak response was observed earlier in high index line (at 14 dpi) as compared to low line (21 dpi). Although, statistically non-significant (P>0.05), the titres were relatively higher in high IC-index line at other dpi too. Sex difference was significant on antibody titre at 28 dpi only; females had higher values. No specific trend could be observed at other dpis. The line x sex interaction was significant at 7 and 28 dpis indicating that differences between sexes across the lines were not similar.