# Identifying the Genetic Basis of Fetal Loss in Cows and Heifers Through a Genome-Wide Association Analysis

## TL;DR

This study identifies genetic regions linked to fetal loss in dairy heifers and cows, offering insights to improve reproductive efficiency in cattle.

## Contribution

The study discovers distinct genetic loci associated with fetal loss in heifers and primiparous cows using GWAA.

## Key findings

- 16 genomic regions and 27 candidate genes were associated with fetal loss in heifers.
- 44 genomic regions and 87 candidate genes were associated with fetal loss in primiparous cows.
- No shared loci were found between heifers and cows or across different inheritance models.

## Abstract

Fetal loss in cattle is defined as a pregnancy loss between day 42 and day 260 of gestation, after which the calf can survive outside of the uterus. Fetal loss negatively impacts cattle health and productivity, and results in substantial economic losses to the dairy industry. This study aimed to better understand the genetic causes of fetal loss in dairy heifers (a female being bred for her first pregnancy) and primiparous cows (a female in her first lactation being bred for a second pregnancy). To account for multiple testing in this genome-wide association analysis (GWAA), associations were evaluated using the false discovery rate (FDR), which represents the expected proportion of false positives among all rejected hypotheses. A total of 16 genomic regions and 27 positional candidate genes were identified as associated (FDR < 0.05) with fetal loss in heifers, and 44 regions and 87 positional candidate genes were identified as associated (FDR < 0.05) with fetal loss in primiparous cows. The identification of these genomic regions and genes associated with fetal loss facilitates selection for cattle that are more reproductively efficient and provides a better understanding of the causes of fetal loss.

Fetal loss, the spontaneous termination of pregnancy between day 42 and 260 of gestation, is poorly understood. Impacts of fetal loss include loss of production, increased health risk, and economic loss. The aims of this study were to identify loci associated with fetal loss in Holstein heifers and primiparous cows to facilitate the selection of reproductively efficient cattle and identify the genetic causes of fetal loss. A genome-wide association analysis (GWAA) compared 5714 heifers that calved at term (controls) to 416 heifers that experienced fetal loss (cases), and for primiparous cows, 2519 controls were compared to 273 cases. The efficient mixed-model association eXpedited approach in the SNP and Variation Suite (v 9.1) statistical software was used with additive, dominant, and recessive inheritance models for the GWAA. In heifers, 16 loci were associated (FDR < 0.05) with fetal loss in the recessive model. In primiparous cows, there were 44 loci associated (FDR < 0.05) with fetal loss in the recessive model. No loci associated with fetal loss were shared between cows and heifers or in the additive and dominant models. These results improve the characterization of genetic factors contributing to fetal loss in Holstein heifers and primiparous cows and provide targets for genomic selection.