Genome-wide association study for polledness, horn shape, and wool traits in Original Valachian sheep

The Original Valachian sheep is an endangered Slovak national breed that is well adapted to high-altitude pastures. The sheep can be horned with various shapes and can have multi-coloured or completely white or black wool. Breeders are interested in learning about the genetic basis of these traits. We conducted a genome-wide association study based on the genomic information of 96 sheep genotyped by the GeneSeek GGP Ovine 50K SNP (single-nucleotide polymorphism) chip and on the following traits: polledness (presence or absence of horns), horn shape, and wool colour (completely white and completely black). The univariate linear mixed model was used to discover genetic variants significantly associated with tested traits. The Bonferroni correction and the false-discovery rate were used as significance thresholds. The RXFP2 gene (chromosome 10, 29.5 Mb) was identified as a strong candidate for polledness. In addition, when compared to animals with sideways-turned horns vs. polled, the region around the ADAMTS3 gene (chromosome 6, 88.47 Mb) was significant. A total of nine significant genomic regions were found when comparing the sideways-turned spiral horns with the backwards-curled horns, the two most frequent horn types in Original Valachian sheep. The RXFP2 may also contribute to the genetic control of horn shape. Genes identified in other regions were involved to osteogenic differentiation and osteoblast proliferation (PCP4, chromosome 1, 260.7 Mb), bone mineral density and mineral content (NKX1-2, chromosome 22, 43.75 Mb). The significant genetic variants close to the region of MC1R (chromosome 14, at 14.2 Mb) were associated with the wool colour of sheep that were fully white or fully black animals. The results of this study will contribute to a better understanding of the phenotypic variability of the Original Valachian sheep, especially regarding traits that are very important for breeders of this endangered breed.