206 GENOME-WIDE ASSOCIATIONS FOR REPRODUCTIVE TRAITS IN RUSSIAN HOLSTEIN POPULATION

Abstract

Reproductive health is an important trait in selection of dairy cattle. A genome-wide association study (GWAS) is a powerful tool for annotating phenotypic effects on the genome and to get knowledge of genes and chromosomal regions associated with reproductive performance (Cole et al. 2011). Combining GWAS and genetic profiling of embryos before implantation enables to develop new strategies to select elite breeding genotypes before transfer (Humblot et al. 2010; Ponsart et al. 2013). The aim of the current study was to evaluate the association between single nucleotide polymorphisms (SNP) and estimated breeding values (EBV) for reproductive traits [interval to insemination (EBVII) and interval between calving (EBVIC)] for Russian Holstein cattle and to evaluate the effect of the biopsy procedure on the viability of bovine embryos produced in vitro as a basis for pre-implantation genetic diagnosis (PGD). Ninty-six progeny-tested sires of artificial insemination station Moscowskoe were selected based on the reliability for EBVII and EBVIC. Estimations of breeding values of sires were performed by best linear unbiased prediction (BLUP) mixed model equations. DNA was extracted from sire semen samples. SNP genotyping was performed using the Illumina BovineSNP50 BeadChip (Illumina Inc., San Diego, CA, USA) containing 54609 SNPs. Quality control information was carried out in PLINK (v. 1.07; Purcell et al. 2007 Am. J. Hum. Genet. 81). Based on the quality control information, 41442 SNPs were selected for subsequent GWAS. We have identified 3270 SNPs having significant effect (P < 0.05) on studied traits. The most significant associations with EBVII were found for SNPs Hapmap38548-BTA-97184 and ARS-BFGL-BAC-11821 with coefficient of determination (R²) of 0.2189 and 0.1937, and P-values 2.27 × 10^–6 and 1.01 × 10^–6, respectively. The most significant effect on EBVIC was detected for SNPs ARS-BFGL-NGS-59769 and ARS-BFGL-NGS-38020 with coefficient of determination (R²) of 0.236 and 0.2421, and P-values 1.49 × 10^–8 and 7.24 × 10^–8, respectively. The highest number of significant associations was found on BTA5, BTA12, BTA19, and BTA14. Bovine embryos were produced in vitro using a standard procedure. Six to 8 cell biopsies were carried out at Day 6.5 after fertilization. The viability of biopsied embryos was evaluated comparing the hatching rates to non-manipulated embryos. The study of embryos viability after biopsy showed that the hatching rate of biopsied embryos (the number of hatched embryos from the number of embryos in stages of late morula and early blastocyte) was 48% comparing to 67% for non-manipulated embryos. Embryo biopsy is not dramatically decreasing embryo viability. Combining our results of association studies, performed on Russian Holstein population, and technique of embryo biopsy will provide us a powerful tool for selection progress.

This research was supported by the Russian Ministry of Education and Science, project No. 2014-14-576-0057-175.