Genetic selection based on antibody response to sheep erythrocytes influences the immunoresponsiveness to IBD vaccine in White leghorn chickens*

Divergent selection was practiced for humoral immune response, estimated as antibody response to sheep RBCs using haemagglutination (HA) test, in IWG genotype, an elite White Leghorn line that has undergone 25 generations of selection for 40-week part period egg production. Six males and thirty-six females at each extreme (high and low) were used as parents of high (HSRBC) and low (LSRBC) lines, respectively. Twenty chicks in the first generation of divergent selection, 10 at high extreme in HSRBC and 10 at low extreme in LSRBC, identified at 5–6 weeks of age by assessing the antibody response to Sheep RBCs, were evaluated for their immunoresponsiveness to IBDV vaccine. Chicks were vaccinated with IBDV vaccine (Intermediate strain, Biomed, India) at day ‘0’. Sera were collected at 7, 14, 21 and 28 dpi, inactivated at 56° C for 30 min. and stored at −20° C. The sera from extreme responders were analyzed for antibody titres against IBDV (vaccine strain) using ELISA. Data were analyzed by least squares analysis to determine the effect of line and sex, which were taken as fixed effects in the model. Least squares mean titres at 7, 14, 21 & 28 dpi were 1430.36±118.97, 2187.54±90.91, 1779.99±126.33 and 1640.80±107.39, respectively in HSRBC line. Corresponding values in LSRBC line were 1419.26±117.77, 1796.76±89.99, 1571.07±125.06 and 1256.55±106.31, respectively. Peak titres were observed at 14 dpi in both the lines. HSRBC line demonstrated higher titres at all dpis than LSRBC, however, the difference was significant at 14 (P<0.01) and 28 (P<0.05) dpi. Although, females had higher titre values than males at all dpi, but the differences were not significant. It was evident that antibody production to IBDV vaccine is influenced by divergent selection for antibody response to sheep RBC. It may be suggested that selection for higher humoral response elicit higher immunoresponsiveness to vaccines like IBDV and this may further be exploited in future breeding programs to augment the genetic resistance to diseases in layer chickens.