THE INFLUENCE OF MAJOR HISTOCOMPATIBILITY COMPLEX GENOTYPES ON RESISTANCE TO PASTEURELLA-MULTOCIDA AND NEWCASTLE-DISEASE VIRUS IN TURKEYS

Sublines homozygous for each of four MHC haplotypes were developed fro m randombred control populations of turkeys and challenged with Pasteu rella multocida (capsular serogroup a, somatic serotype 3, 4) at 6 wk of age or Newcastle disease virus (NDV; Texas GB strain) at 4 wk of ag e. In addition, individuals from a randombred control line (RBC2) and a subline (F) of RBC2 long-term selected for increased 16-wk BW were i ncluded in most of the challenge trials. The duration of the challenge trials was 2 wk for both organisms. Mortality following challenge wit h P. multocida or NDV was higher in the F line than in its randombred control. The MHC genotypes differed in mortality following exposure to both organisms but the rankings of the genotypes were not the same fo r P. multocida and NDV. The increased susceptibility of the F line to both organisms could not be explained by known changes in the frequenc y of the MHC haplotypes.