Genome-Wide Association Analyses of Fertility Traits in Beef Heifers.

Morgan R Stegemiller,Brenda M Murdoch,Troy N Rowan,Gordon K Murdoch,Gabrielle M Becker,John B Hall,Kimberly M Davenport

doi:10.3390/genes12020217

Morgan R Stegemiller, Brenda M Murdoch + Show 5 more

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https://doi.org/10.3390/genes12020217

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Abstract

The ability of livestock to reproduce efficiently is critical to the sustainability of animal agriculture. Antral follicle count (AFC) and reproductive tract scores (RTS) can be used to estimate fertility in beef heifers, but the genetic mechanisms influencing variation in these measures are not well understood. Two genome-wide association studies (GWAS) were conducted to identify the significant loci associated with these traits. In total, 293 crossbred beef heifers were genotyped on the Bovine GGP 50K chip and genotypes were imputed to 836,121 markers. A GWAS was performed with the AFC phenotype for 217 heifers with a multi-locus mixed model, conducted using the year, age at time of sampling and principal component analysis groupings as the covariates. The RTS GWAS was performed with 289 heifers using an additive correlation/trend test comparing prepubertal to pubertal heifers. The loci on chromosomes 2, 3 and 23 were significant in the AFC GWAS and the loci on chromosomes 2, 8, 10 and 11 were significant in the RTS GWAS. The significant region on chromosome 2 was similar between both analyses. These regions contained genes associated with cell proliferation, transcription, apoptosis and development. This study proposes candidate genes for beef cattle fertility, although future research is needed to elucidate the precise mechanisms.

Highlights

Cattle producers benefit from animals that reproduce reliably and efficiently, making fertility a critical trait in the cattle industry
Group 1 consists of heifers that were sired by a single SimAngus sire and Group 2 are heifers sired by six Hereford bulls
The genome-wide association studies (GWAS) identified three regions significantly associated with the antral follicle count (AFC) and four associated with the reproductive tract scores (RTS) in crossbred heifers

Summary

Introduction

Cattle producers benefit from animals that reproduce reliably and efficiently, making fertility a critical trait in the cattle industry. Improving reproductive efficiency can be accomplished by selecting replacement heifers with higher fertility and a longer reproductive life span. There are several measures used to estimate fertility, including Anti-Müllerian hormone concentration, days open and calving performance: this study focuses on the antral follicle count (AFC) and reproductive tract scores (RTS). Cattle with a higher AFC tend to have ovaries of significantly greater length, size and weight [7]. Ovaries with a greater number of antral follicles indicate a larger ovarian reserve (OR) [8]. Bos taurus, Bos indicus and Bos indicus-taurus animals that have higher AFC produce more oocytes during superovulation [2,4,5]. Previous studies in Bos taurus crossbred beef heifers and Holstein-Friesian dairy cows have shown that animals with a high AFC are more likely to be pregnant at the end of breeding season [8,10]

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