Loci associated with conception rate in crossbred beef heifers

Abstract

The inability of beef cattle to maintain full term pregnancies has become an economic concern for the beef industry. Herd management and nutritional improvements have alleviated environmental impacts on embryonic and fetal loss, yet additional gains can be made through genomic selection. The objectives of this study were to identify loci and gene-sets in crossbred beef heifers associated with the number of services required to become pregnant (TBRD) and heifer conception rate at first service (HCR1). Heifers (n = 709) from a commercial beef operation underwent one round of artificial insemination, before exposure to bulls for natural service for 50 days. Pregnancy and time of conception was determined by ultrasound 35 days after the breeding season. Heifers were genotyped using the GeneSeek (Lincoln, NE) Bovine GGP50K BeadChip prior to genome-wide association analyses (GWAA) conducted using an EIGENSTRAT-like model to identify loci associated (P < 1 × 10 −5) with TBRD and HCR1. One locus was associated (P = 8.97 × 10 −6) with TBRD on BTA19 and included the positional candidate gene ASIC2, which is differentially expressed in the endometrium of fertility classified heifers, and the positional candidate gene, SPACA3. Gene-set enrichment analyses using SNP (GSEA-SNP) data, was performed and identified one gene-set, oxidoreductase activity, acting on paired donors, with incorporation or reduction of molecular oxygen as enriched (NES = 3.15) with TBRD and contained nine leading edge genes that contributed to the enrichment of the gene set. The enriched gene-set is involved in catalyzing oxidation-reduction reactions, which have been associated with oxidative stressors impacting pregnancy success. No loci were associated nor gene-sets enriched with HCR1. Identification of loci, positional candidate genes, gene-sets and leading edge genes enriched for fertility facilitate genomic selection that allows producers to select for reproductively superior cattle, reduce costs associated with infertility, and increase percent calf crop.

Assessment of Plasma Oxidative Stress Biomarkers and Metabolic Parameters of Dairy Heifers: Relationship with Success at First Service

“…This set of genes was involved in the catalysis of redox reactions, which have been associated with oxidative stressors having an impact on successful gestation. However, no loci were associated or any amplified gene set in the rate of conception at first service (Oliver et al, 2020). Furthermore, GST, GSH and GPx are essential indicators for evaluating the antioxidant system in plasma and they complement each other as they are dependent on glutathione.…”

“…Celi et al (2012) suggested that changes in plasma biomarkers of oxidative stress could not quantitatively reflect the modifications due to stress in reproductive tissues. Recently, Oliver et al (2020) identified in beef heifers a set of genes that are expressed in the endometrium of heifers, by acting on the increase in oxidoreductase activity with the number of services required for become pregnant. This set of genes was involved in the catalysis of redox reactions, which have been associated with oxidative stressors having an impact on successful gestation.…”

Identification of quantitative trait loci and associated candidate genes for pregnancy success in Angus–Brahman crossbred heifers

“…There have been several studies reporting use of GWAS to identify quantitative trait loci (QTLs) for fertility traits of beef cattle. Among these studies are GWAS for age at first calving [ 16 – 18 ], pregnancy to AI after estrous synchronization [ 10 ] or after fixed-time AI [ 12 ], pregnancy outcome at the end of the breeding season [ 11 ], conception rate and number of services required for pregnancy [ 19 , 20 ], rebreeding success after calving [ 21 ], and fertility classification following serial embryo transfers [ 22 ].…”