Genome-wide Association Study and in Silico Functional Analysis of the Number of Embryos Produced by Holstein Donors

Superovulation or ovum pick-up and in vitro fertilization are technologies used to produce an increased number of embryos from elite females. Embryo production traits have been shown to be heritable, but the genes that cause this variability have not yet been assessed. The main objectives of this study were to perform a genome-wide association study (GWAS) to find single nucleotide polymorphisms (SNP) associated with embryo production traits and to identify candidate genes affecting the number of embryos produced by Holstein donors in Canada that may provide insight into the regulation of embryo production. Breeding values were estimated and de-regressed for all donors and sires using a data set of 150,971 records of superovulation or ovum pick-up and in vitro fertilization. A total of 11,607 animals were genotyped, but of that number only 5,118 were genotyped with at least a 50K SNP panel and had a de-regressed estimated breeding value reliability of at least 10%. For the GWAS, 606,406 imputed SNP on 29 autosomal chromosomes were considered after applying quality control measures. A single-SNP univariate mixed linear animal model was used to perform the GWAS, and a 5% false discovery rate was applied to adjust for multiple testing. We found 36 and 14 significant SNP associated with the total number of embryos and the number of viable embryos, respectively, with most of them located on chromosome 11. Using these significant SNP, positional genes located within 10,000 bp upstream and downstream of the SNP were retrieved. Thirteen genes were harboring or near the significant SNP for the total number of embryos, 4 of them also being near the significant SNP for viable embryos. Some of these genes (CRB2, DENND1A, MAD1L1, NDUFA8, PTGS1) could be considered as potential positional candidate genes related to the number of embryos produced by a donor. This list will need to be validated in an independent population to confirm the role of the genes for embryo production.