Prenatal Establishment Of The Foal Gut Microbiota: A Critique Of The In Utero Colonisation Hypothesis

Bacteria colonisation of the foal's gastrointestinal tract (GIT) is a critical developmental stage, effecting subsequent immunological and health outcomes. It has long been thought that the equine fetus develops in a sterile intrauterine environment and GIT colonisation commences at birth. Research now suggests that bacteria isolated from amniotic fluid are the initial colonisers of the fetal GIT, and exposure to the dam's microbiota and the external environment during birth provide supplementary colonisation. This in utero colonisation hypothesis has only recently been examined in the horse and microbiota were detected in the amniotic fluid and meconium of healthy equine pregnancies. This review highlights the possible colonisation routes of these bacteria into the fetal compartments and examines their likely origins from the existing maternal microbiome. However, the current data describing the amniotic microbiota of the horse are limited and there is a need for research to fill this gap. Understanding the significance of intrauterine microbes for foal GIT colonisation may provide strategies to improve neonatal health.