Improving disease resistance in chickens: divergent selection on natural antibodies

Natural antibodies (NAb) are antibodies recognizing antigens without previous exposure to this antigen. Keyhole limpet hemocyanin (KLH)-binding NAb titers in chickens are heritable, and higher KLH-binding NAb titers have been associated with higher survival. This suggests that breeding for higher NAb titers might improve general disease resistance. A purebred White Leghorn chicken line was divergently selected and bred on total KLH-binding NAb titers at 16 weeks of age for 6 generations, and resulted in a High and Low line. The average estimated breeding value differences in KLH-binding NAb titers increased with 0.36 for total, 0.40 for IgM, and 0.32 for IgG per generation. Generations 4 and 6 of the selection lines were inoculated with an avian pathogenic Escherichia coli (APEC) at 8 days of age. Mortality and morbidity after 1 week were signicantly reduced in the High line compared to the Low line, which suggests a higher APEC resistance in the High line compared to the Low line. To investigate possible correlated responses on the immune system, several traits were measured at different ages in several generations: the High line showed higher different NAb titers at different ages, antibody concentrations, percentage of antibody-producing B cells, and bursa weight at young age compared to the Low line. This suggests that KLH-binding NAb selection has a favourable correlated response on the humoral adaptive immune system. No line differences were observed for T cells, γδ T cells, natural killer (NK) cells, and antigen-presenting cells (APC). This might indicate that the selection had no unfavourable correlated responses on other parts of the immune system. This selection experiment shows that selective breeding on total KLH-binding NAb titers at 16 weeks of age is possible, and that selection for higher NAb has a benecial effect on resistance to APEC infection. In addition, the selection experiment suggests a promising opportunity for improving general disease resistance without unfavourable correlated selection responses.