Simple SummaryAlthough previously the placenta was assumed to be sterile, with microbes only being present in association with pathology, recent studies have suggested that this assumption may not be correct. Some researchers argue for the presence of a microbial community in the placenta, which is important to help the foal to adapt to life outside the uterus. Therefore, we examined the placenta, amniotic fluid and umbilical blood of 24 foaling mares, as well as jugular blood from the foals. All of the mares and foals were healthy, and foaling was normal. Some bacterial growth was isolated in most of the umbilical blood samples. Bacterial DNA was extracted and sequenced from placental samples. The most abundant phyla were Proteobacteria (approximately 44%) and Actinobacteria (approximately 28%). In conclusion, bacteria were found in the fetal compartments and placenta of healthy equine pregnancies, perhaps lending support to the theory that the placenta has its own bacterial community.AbstractThe presence of a microbiome/microbiota in the placenta is hotly debated. In previous studies, the presence of bacteria in equine amniotic fluid and umbilical blood was independent of foal health. The objective of the present study was to determine if the same bacteria are present in the equine placenta as in amniotic fluid and umbilical blood. Samples were obtained from 24 parturient mares and foals. Placental bacterial DNA was extracted, and the microbiome was identified using 16S rRNA sequencing. All amniotic fluid samples contained some polymorphonucleocytes; bacteria were isolated from four samples. Aerobic or anaerobic growth was found in 18 and 3 umbilical blood samples, respectively. Serum amyloid A was <5 mg/L in all 24 samples, total WBC varied between 2900 and 10,700/µL, and fibrinogen varied between 0 and 5.16 g/L. In jugular blood, serum amyloid A was <5 mg/L in all 24 foals, total white blood count was 3200 to 8100/µL, and fibrinogen was 0.44 to 4.42 g/L. The diversity of bacterial microbiota was similar in all placental regions at the phylum level but differed at the genus level; the most abundant phyla were Proteobacteria (42–46.26%) and Actinobacteria (26.91–29.96%). In conclusion, bacteria were found in the fetal compartments and placenta of healthy equine pregnancies; however, we can neither prove nor disprove the hypothesis that the placenta has its own microbiome.