# Vaginal Microbiome Is Associated with Breed and Pregnancy Status in Beef Cattle

## TL;DR

This study found that the vaginal microbiome in beef cattle varies by breed and pregnancy status, suggesting a potential link to fertility.

## Contribution

The study reveals breed- and pregnancy-specific differences in the vaginal microbiome of beef cattle.

## Key findings

- Line 1 cows showed significant differences in microbial diversity compared to other breeds.
- Pregnancy status influenced microbial diversity in Line 1 cows.
- Ureaplasma and Mycoplasma were more common in Line 1, while uncultured bacteria were more prevalent in non-pregnant cows.

## Abstract

Reproductive failure is a large economic burden on cattle production; therefore, identifying factors that affect fertility is important to improve livestock profitability. In this study, vaginal microbiomes of seventy-four beef cows from three genetic groups (Angus, Hereford Line 1, and crossbreds) were examined using 16S rRNA sequencing. The Line 1 cows differed significantly from the other groups in multiple diversity measures. Moreover, pregnancy status influenced diversity within Line 1. Overall, microbial community composition was affected by genetic group and pregnancy status. Each breed had distinct OTU profiles: Line 1 had higher Ureaplasma and Mycoplasma, and some uncultured bacteria were more common in non-pregnant cows. The findings show breed- and pregnancy-associated differences in vaginal microbiomes and warrant further research to determine drivers and fertility associations.

Reproductive performance is a key determinant of overall livestock productivity. In both beef and dairy systems, reproductive failure represents a leading cause of cow culling. Reproductive traits are complex in nature and present a low heritability in general. Additionally, the collection of such phenotypes usually relies on indirect measures of fertility, such as conception success. Therefore, further investigation into genetic and non-genetic factors of reproductive traits in cattle is necessary. The hosts’ microbiome plays a crucial role in vertebrate biology, including reproduction. We, therefore, hypothesize that microbiome indicators may serve as a biomarker of fertility. This study explored the relationship between vaginal microbiome profiles and pregnancy among three beef cattle genetic groups using field data. Vaginal swabs were collected from 74 cows at Fort Keogh, MT, including 23 Angus, 23 Hereford Line 1, and 28 crossbreds, and DNA was extracted and analyzed via 16S rRNA gene amplification. Significant differences in alpha diversity (p < 0.05) were found among Line 1 cows compared to Angus and crossbreds in many indicators of alpha diversity. Pregnancy status did not influence alpha diversity of samples significantly, but trends toward significance were observed. PERMANOVA analysis indicated that genetic groups and pregnancy status affected microbial composition (p < 0.05), but their interaction was not significant. Each genetic group showed unique compositions of operational taxonomic units (OTUs), with higher proportions of Ureaplasma and Mycoplasma families in Line 1. Additionally, variations in microbial communities were observed between pregnant and non-pregnant cows, with certain uncultured bacteria more prevalent in non-pregnant cows. While field data are useful for such studies and represent a real production system, better-designed experiments are necessary to validate findings and test hypotheses. These results suggest variation in vaginal microbiomes across breeds and pregnancy status, emphasizing the need for further research to identify factors affecting these changes.