Genetic differences in susceptibility of chicken lines to infection with infectious bursal disease virus

Mortality rates in 11 inbred and partially inbred chicken lines inoculated with a very virulent strain (CS89) of infectious bursal disease virus (IBDV) varied considerably, being highest (almost 80%) in a Brown Leghorn line (BrL). Bursa of Fabricius to body weight ratios were depressed in the survivors in each line, but no differences were observed between lines. However, histological examination of bursae from survivors showed that, although bursal damage occurred in every line, it was most severe in the two lines (BrL and White Leghorn W1) in which the highest mortality was recorded. Experiments with F1 matings between highly susceptible and highly resistant lines showed that resistance was partially dominant and that there were no maternal effects. Experiments using F2 and backcross chicks suggested the involvement of a single gene and indicated no involvement of the MHC. There was considerable variation between lines in IBDV-specific antibody, measured by ELISA, both in the vaccinated parent hens and in the amounts of inherited maternal antibody and its rate of decay in the progeny.