QTL Mapping for Body Weights and Calving Ease in Hereford Cattle Using 1Mb SNP Windows and Bayesian Inference

In beef cattle, body weight and its related trait calving ease are important traits and optimizing size at various ages is of key economic interest. This study mapped QTL for birth, weaning and yearling weights, and calving ease in Hereford beef cattle using a BayesB approach in GenSel software with 1Mb SNP windows. Some 1,081 animals including sires and dams were genotyped with the Illumina BovineSNP50 BeadChip. De-regressed breeding values were used as observations to estimate SNP effects. Estimated effects of SNPs classified into 1Mb windows were used to compute breeding values and the corresponding percentage of genetic variance explained by every such window. A window explaining more than 1% of genetic variance was considered to be a QTL.  Three regions located at 4Mb of BTA20, 38Mb of BTA6, and 93Mb of BTA7 (UMD3.1 assembly) were identified for birth weight. Two of these QTL (4Mb of BTA20 and 93Mb of BTA7) were identified for weaning and yearling weights, and the third QTL (38Mb of BTA6) was identified for calving ease. The cumulative genetic variance of identified QTLs were 19%, 11%, 14% and 19% for birth, weaning and yearling weights, and calving ease, respectively. We found very promising candidate genes (SH3PHD2B, NCAPG and ARRDC3) in each of these three regions. Further genotyping and statistical analyses are needed to find the casual mutations. Once found, knowledge of such mutations would create new opportunities for the selection of animals with appropriate body weight and decreased dystocia.