Estimation of crossbreeding parameters for humoral response in broiler

• We assessed antibody response to sheep erythrocytes and serum haemolytic complement.
• We estimated crossbreeding parameters for the traits with a complete diallel design.
• Estimates of different crossbreeding parameters were statistically significant.
• Additive and non-additive genes contribute to variations in humoral immune response.
• Selection for immune traits requires formation of specialised or index-based lines.

Crossbreeding parameters for humoral immune response – including the antibody production to sheep red blood cell challenge (SRBC) and serum haemolytic complement level (HC) – were estimated using a complete 4×4 diallel design with four synthetic broiler lines namely coloured synthetic male line (CM), white synthetic male line (WM), coloured synthetic female line (CF) and naked neck line (NN). The genetic group had a strong effect (P<0.01) on the mean SRBC and HC. Among 16 genetic groups, with 4 purebred and 12 crossbred groups, the crossbred progenies of NN×CM and CM×WM produced the highest mean SRBC (10.59±0.53) and HC (6.37±0.20), respectively. Estimates of direct line effect and maternal genetic effect for both SRBC and HC; average heterosis, direct line heterosis, and specific combining ability for HC were statistically significant (P<0.05). Most crossbred groups exhibited positive overall heterosis for both traits. Crossbred groups of WM×CM and CM×WM recorded the highest estimates of mean and percentage heterosis for SRBC (2.65 and 38.93%) and HC (1.72 and 36.84%), respectively. Results indicated that both additive and non-additive genetic variations were important for the humoral immune response in broiler. Differences in rankings of lines and crosses with respect to crossbreeding parameters suggested that genetic variations to these traits can be exploited by selection of specialised lines on the basis of response to SRBC challenge and serum HC level, or formation of a line based on optimum index values for both traits.