Resistance to Marek's disease virus in white leghorn chickens: Effects of avian leukosis virus infection genotype, reciprocal mating, and major histocompatibility complex

Genetic improvement for resistance to Marek's Disease (MD) in chickens cont inues to be of interest to the poultry industry. The aims of this study wer e to identify effects of the MHC on the molecular level and of avian leukos is virus (ALV) resistance status on MD mortality in two noninbred White Leg horn chicken lines that differ in B blood group type. Previously, within ea ch of the chicken lines, sublines had been selected for resistance or susce ptibility to ALV infection with Subgroups A and B. In this study, F-2 offsp ring, obtained by crossing the two ALV-resistant or the two ALV-susceptible sublines, were tested for MD mortality after contact exposure at 1 d of ag e. Reciprocal matings were made in the grandparental generation. The MD mor tality percentages, in an observation period of 17 wk, of F-2 offspring fro m two hatches were 82.63 and 92.35%, respectively. Survival analysis (Cox m odel) was applied to assess the risk of dying from MD. No differences in MD mortality risk profiles were found between ALV-resistant and ALV-susceptib le F-2 offspring. Within ALV-susceptible F-2 offspring, however, a reciproc al mating effect was observed in both hatches. The MHC Class I, II, and IV restriction fragment length polymorphism (RFLP) analyses were carried out o n birds of the first hatch. Although two of 11 MHC class IV RFLP bands disp layed a significant effect, in general, a strong association of MHC and MD mortality was not detectable.