Reproductive Microbiomes in Domestic Livestock: Insights Utilizing 16S rRNA Gene Amplicon Community Sequencing

SIMPLE SUMMARY: The reproductive microbiome includes bacterial colonies within the vagina, uterus, placental tissues and fluids, semen, and milk. Assessments of the human reproductive microbiome have established commensal and pathogenic bacteria that can influence fertility. Reproductive efficiency in domestic livestock species (dairy and beef cattle, swine, sheep and goats, and horses) is also impacted by bacterial presence and abundance within the reproductive tract of both males and females. However, advancements from culture-based methods of bacterial identification to specific sequencing of the 16S rRNA gene have only recently begun to establish this interconnected relationship. Thus, this review aims to discuss the most recent overview of reproductive microbial identification in domestic livestock species utilizing 16S rRNA gene sequencing and its potential roles in fertility. ABSTRACT: Advancements in 16S rRNA gene amplicon community sequencing have vastly expanded our understanding of the reproductive microbiome and its role in fertility. In humans, Lactobacillus is the overwhelmingly dominant bacteria within reproductive tissues and is known to be commensal and an indicator of fertility in women and men. It is also known that Lactobacillus is not as largely abundant in the reproductive tissues of domestic livestock species. Thus, the objective of this review is to summarize the research to date on both female and male reproductive microbiomes in domestic livestock species (i.e., dairy cattle, beef cattle, swine, small ruminants, and horses). Having a comprehensive understanding of reproductive microbiota and its role in modulating physiological functions will aid in the development of management and therapeutic strategies to improve reproductive efficiency.