Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 13, 2005
Publication Date: March 2, 2006
Citation: Isler, B.J., Freking, B.A., Thallman, R.M., Heaton, M.P., Leymaster, K.A. 2006. Evaluation of associations between prion haplotypes and growth, carcass, and meat quality traits in a Dorset x Romanov sheep population. Journal of Animal Science. 84:783-788. Interpretive Summary: Elimination of transmissible spongiform ecephalopathies, such as BSE in cattle and scrapie in sheep, is critical to maintain consumer confidence in food safety. Genetic markers associated with scrapie resistance are used to reduce the incidence of scrapie in sheep populations worldwide. However, before breeding programs focus on intensive selection for scrapie resistance, it is important to investigate whether or not selection for resistance to scrapie will adversely affect economically important traits. We found very little evidence of antagonistic relationships between genetic markers for resistance and growth, carcass, and meat quality traits in Dorset and Romanov sheep. Within the Dorset and Romanov breeds, advantages of selection for scrapie resistance while also limiting the level of inbreeding, seem to far outweigh adverse correlated responses that may occur.
Technical Abstract: Within the sheep industry, there is concern about potential antagonistic correlated responses due to intensive selection for scrapie-resistant haplotypes of the prion (PRNP) gene. 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 a F2 Dorset x Romanov population (n = 415) segregating the two callipyge alleles. Haplotypes of the three PRNP codons were determined for each sheep, and breed of origin of each gamete was predicted by genotyping six microsatellite markers flanking the PRNP locus. A total of 25 growth, carcass, and meat quality traits were collected. Data were analyzed using a basic model consisting of fixed effects of year, sex, and callipyge genotype, random effect of sire, and seven 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. For carcass traits, the model contained the linear and quadratic effects of chilled carcass weight and interactions between 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. Within each breed of origin, a contrast between the resistant ARR haplotype and the average effect of other PRNP haplotypes was tested to estimate effects of selection for ARR. There was limited evidence that selecting for scrapie resistance will cause correlated responses due to linkage disequilibrium. Only three traits were significantly associated with PRNP haplotypes in either breed of origin. No significant contrasts were detected for Dorset. 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. This study is the first to account for breed of origin while investigating haplotype associations in a F2 population. This study provided limited evidence of associations between PRNP haplotypes and growth, carcass, and meat quality traits.