Selection for short oviposition interval, avianleukosis virus infection and major histocompatibility complex

Shedding of group-specific antigen of avian leukosis virus(ALV) into egg albumen and the B-blood group(the major histocompatibility complex (MHC) in the chicken) were determined in three Australorp lines:AS line that had been selected primarily for short oviposition interval, ASS line that had been derived from the AS line and developed as a commercial dam line for egg laying, and AC line that had been kept as a randombred control. The proportion of shedders was much higher in the selection lines than in the control line:13.1-16.7% in the AS line, 16.3% in the ASS line in 1984 (before culling of the shedders), and 6.1% and 6.6% in the AC line in 1984 and 1988, respectively. In the AS line, the shedders were 0.24h shorter in oviposition interval than the nonshedders and hence favoured by the artificial selection. This apperared to be responsible for the higher levels of infection in the selection lines. Three haplotypes of the MHC (B8a, B9a and B21) were segregating in the three lines:their respective frequencies were 66.1, 16.2 and 17.7% in AS, 34.5, 21.6 and 43.9% in ASS, and 42.7, 2.0 and 55.3% in AC. Only among the progenies of dams not shedding gs-antigens, the relative risk of a pullet becoming a gs-antigen shedder was different between MHC haplotypes (0.67, 0.48 and 2.53 for B8a, B9a and B21, respectively), suggesting that the three haplotypes were different in susceptibility to horizontal infection from other infected birds. The three MHC haplotypes were also different in average effect on oviposition interval. The average effects estimated from gs-antigen non-shedders in lines AS and ASS over 1987-89 were -0.116 and 0.096 hour for B9a and B21, respectively, relative to zero for B8a.