Comparing the maternal-fetal microbiome of humans and cattle: a translational assessment of the reproductive, placental, and fetal gut microbiomes

Despite differences in gut physiology and morphology, both humans and cattle require a functional gut microbiome in early life. Evidence suggests that both species acquire gut microbes prior to birth, likely from a maternal source, indicating the use of similar mechanisms and timing for fetal gut colonization. Unlike mouse models, cattle share a similar gestation length, parity, and placental microbiome characteristics to humans. The large size of calves allow for contamination-protected sampling of the gut, vagina, and uterus, which would typically require invasive procedures in human cohorts. The ruminant placenta also exhibits a larger degree of separation between maternal and fetal physiology, necessitating a direct and explicit route by which microbes may access the fetal gut. These and other features permit cattle to act as a translational model for early gut colonization. However, cattle do not share similar placental morphology, gut function, or early immune system interactions with humans, creating barriers to their use as a biomedical model. Identifying similarities and differences between humans and cattle may outline the most important functions of the placental and fetal gut microbiomes, indicate the source of these microbes, and highlight the role of maternal or environmental influences upon fetal health across species. An analysis of sites within the maternal reproductive microbiome that potentially contribute to fetal gut microbial colonization, with a special focus on the comparison between humans and cattle.