Genomics of heifer pregnancy, days open, and days to conception in Red Angus heifers

Although it is challenging to collect information on reproductive traits, fertility traits are believed to play a significant role in the growth of the beef industry and bring revenue to the producers. It has been challenging to make genetic improvement of fertility traits because of scarce records and their low heritability. The joint analyses of economic and indicator traits provided much information for the analysis of other production traits, resulting in favorable improvement. The same method can be applied to reproductive traits to increase prediction accuracy. Furthermore, the ubiquity of high-throughput genotypes and the development of advanced computational methods give hope that there is a possibility of determining the genetic influence on fertility traits. The advancement in phenotypic collection technology eases the keeping of records on both economic and indicator fertility traits. Also, it allows the development of new traits to be analyzed while reducing the cost of data availability. Heifer Pregnancy (HP) - the ability for a heifer to conceive by the end of the breeding season; Days Open (DO) - days of breeding season a heifer remained open; and Days to Conception (DC) -- the number of days it took for a heifer to get pregnant, are easy to measure fertility traits with enough information to make beef reproductive genetic improvement in the industry. The objective of the current study is to identify DNA markers tagging genes influencing HP, DC, and DC among 18,039 Red Angus heifers, find the genetic relationship among those traits, and creating the genomic predictions of days to conception and days open. The results show a small heritability of 0.119 to 0.131, 0.10 to 0.102, and 0.0749 to 0.112 for HP, DO, and DC, respectively. The DC model resulted in higher accuracy than other models. There was a high correlation between HP and DO (r = - 0.61 and 0.85 from the linear model and the liability scale model, respectively). The de-regressed estimated breeding value (EBV) genomewide association (GWAS) yielded 58 and 2 significant SNPs at suggestive significant level (pvalue [less than] 1.0e-05) for HP and DC, respectively. This study found GRID2 and ZMIZ1 genes to be associated with heifer pregnancy, and it has been speculated that the central nervous system related genes ontology and the hormones it controls might suggest the physiology behind some of the reproductive differences. The present study confirms the low heritability status of fertility traits and shows the possibilities of genetic enhancement based on the obtained accuracies. The identified genes and gene terms will serve as starting points for future studies that might focus on different phenotypes while reducing the cost of phenotyping and improving the accuracy of fertility traits genomic predictions.