The Reproductive Microbiome: A Hidden Regulator of Fertility in Domestic Animals

Abstract

Researchers have long attributed the reproductive capability of domesticated animals primarily to genetics, hormonal interplay, nutrition, and animal management. Now, the new breakthroughs in high-throughput sequencing technologies have identified another important factor - the reproductive microbiome. In particular, it was revealed that the microbial communities of both the male and the female reproductive tracts have active interfaces with host immunity, hormone signalling, gametes, and embryos. The seminal microbiome of bulls, boars, stallions, and bucks has been linked to sperm motility, morphology, and fertilizing capacity, and, because artificial insemination deposits semen-borne bacteria into the female tract, seminal and female-tract communities can interact to influence conception outcomes. The new data received from different livestock species show that the maintenance of normal microbiota is important for uterine health, semen quality, fertilization, implantation, and the maintenance of pregnancy, whereas changes in the microbiome composition are characteristic of infertility, post-partum uterine disease, repeat breeding syndrome, and early loss of embryos. However, most of this evidence remains associative: confounding by parity, metabolic status, hygiene, and antibiotic use, together with contamination of low-biomass samples, means that causal links between specific taxa and fertility are still largely unproven. Although many questions are still unclear, the development of microbiome studies is changing reproductive biology rapidly and opening new perspectives for precision veterinary medicine. The current article is devoted to a review of recent advances in microbiome research in reproduction and the discussion of their applications in practice by veterinarians and livestock producers.