Evaluation of associations between prion haplotypes and growth, carcass, and meat quality traits in a Dorset x Romanov sheep population.

There is concern about potential antagonistic correlated responses due to intensive selection for scrapie-resistant haplotypes of the prion (PRNP) gene in sheep. The objective of the present research was to test for associations of PRNP haplotypes for codons 136, 154, and 171 with growth, carcass, and meat quality traits in an F2 Dorset x Romanov population (n = 415) segregating the 2 callipyge alleles. Haplotypes of the 3 PRNP codons were determined for each sheep, and breed of origin of each gamete was predicted by genotyping 6 microsatellite markers flanking the PRNP locus. Twenty-five growth, carcass, and meat quality traits were evaluated. Data were analyzed using a basic model consisting of fixed effects of year, sex, and callipyge genotype, the random effect of sire, and 7 covariates corresponding to the probability that a lamb inherited a specific PRNP haplotype of either Dorset or Romanov origin. A fixed effect of litter size was added to the model for growth traits. The model for carcass traits contained the linear and quadratic effects of chilled carcass weight and the interactions among callipyge genotype and linear and quadratic terms. For meat quality traits, the model contained chilled carcass weight as a covariate and the interaction between callipyge genotype and chilled carcass weight. A contrast between the resistant ARR haplotype and the average effect of other PRNP haplotypes was tested to investigate the effects of potential selection for ARR within each breed of origin (Dorset, ARR vs. ARQ, VRQ, and AHQ; Romanov, ARR vs. ARQ and VRQ). There was limited evidence that selecting for scrapie resistance would cause correlated responses due to linkage disequilibrium. Associations of only 3 traits with PRNP haplotypes were detected in either breed of origin. In Romanov, the ARR haplotype was associated with longer carcasses (P < 0.013), narrower rumps (P = 0.038), and less marbling (P = 0.022) than the average of ARQ and VRQ haplotypes. No significant contrasts were detected for Dorset. This study is the first to account for breed of origin while investigating haplotype associations in an F2 population. This study provided limited evidence of associations between PRNP haplotypes and growth, carcass, and meat quality traits.