Add time:08/02/2019         Source:sciencedirect.com

The black merino variety is an emerging fine-wool merino breed variety of sheep. Their flocks have been reared in Portugal and Spain under different criteria regarding the selection for scrapie resistance haplotypes. This study was aimed to report for the first time in the black merino the prion protein (PRNP) haplotype frequency distribution using sequencing. A sample of 120 sheep belonging to four flocks was analyzed in this study. Three unselected flocks from Portugal and one selected for ARR/ARR genotypes from Spain. The number of polymorphism sites was extended here from three positions (136, 154 and 171) to five by adding the positions 141 and 143 due to both to show its current intermediate frequency in Portuguese sheep and to study the genetic relationship among haplotypes using networks analysis. In this way susceptibility to classical and atypical scrapie can be elucidated. Eight haplotypes could be reported in the black merino as follows: ALHRR, ALHRQ, ALRRQ, ALHHQ, AFHRQ, ALHRH, VLHRQ and T112ALHRQ but the last was a singleton haplotype. The results showed high genetic differentiation among flocks due to an unbalanced frequency distribution of haplotypes suggesting scarce genetic flow among them in Portugal. After collapse haplotypes to three positions (136, 154 and 171) the black merino from Portugal showed similar haplotype frequencies than in previous study except for the VRQ haplotypes with higher frequency in this study. The finding of AFHRQ was interesting because it was associated to atypical scrapie being the only cases declared in Portugal of this disease. In conclusion, we reported high richness in haplotypes in this sheep, but its distribution critically depends on the studied flock. This genetic richness enables to analyze different scenarios before implemented breeding programmes. In this way the application of a breeding programme to control scrapie appears to be a less challenging task.

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