Metagenomic characterization of the equine endometrial microbiome during anestrus.

Overview

• This study examined the microbial communities in the uterus of healthy mares during two different reproductive stages: estrus (when mares are fertile) and anestrus (the non-breeding season).
• Using genetic sequencing methods, the research found significant differences in the diversity and composition of uterine bacteria between these stages, suggesting that the mare’s reproductive cycle influences the uterine microbiome.

Background

• The equine uterus is usually studied during estrus due to its importance for breeding and pregnancy establishment.
• High levels of estrogen during estrus influence the uterine environment and presumably its microbiome—the community of bacteria present.
• The vaginal microbiome in horses remains relatively stable throughout the reproductive cycle, but it was previously unknown if the uterine microbiome changes with cyclicity.

Research Hypothesis and Aim

• Hypothesis: The uterine microbiome differs between estrus and anestrus in mares.
• Goals:
  • Characterize the resident endometrial microbiome during anestrus (non-breeding season).
  • Compare the anestrus microbiome to that present during estrus.

Methodology

• Sample Collection:
  • Endometrial swabs taken from 16 healthy mares during estrus.
  • Swabs taken from the same or similar group of mares during anestrus (8 mares).
  • Sampling used double-guarded swabs to minimize contamination.
• Microbial Identification:
  • 16S rRNA gene sequencing employed to identify and classify bacteria present in samples.
  • This method allows detection of a broad range of bacteria by targeting a conserved genetic marker.

Key Findings

• Microbial Diversity and Richness:
  • The uterine microbiome during estrus showed low bacterial diversity and richness—fewer types of bacteria and less variety overall.
  • During anestrus, both diversity (variety of bacterial species) and richness (number of species) were significantly higher compared to estrus.
• Dominant Bacterial Groups:
  • Despite differences in diversity, both estrus and anestrus endometrial microbiomes were mainly composed of Proteobacteria, Firmicutes, and Bacteroidota phyla.
  • This suggests core bacterial groups remain relatively stable, but their abundance and community structure shift between cycle stages.
• Microbial Community Composition:
  • Statistical analyses demonstrated significant differences in the overall bacterial community structure between estrus and anestrus samples.

Interpretations and Implications

• The changes in the uterine microbiome may be influenced by hormonal shifts and the immune environment during the reproductive cycle.
• The estrus uterine environment, influenced by high estrogen, may favor fewer bacterial species, possibly to prepare for pregnancy or prevent infection.
• During anestrus, the immune system and uterine environment may allow for a more diverse bacterial population.
• Understanding these differences could improve reproductive management and health monitoring in horses.

Future Directions

• Functional studies are needed to determine the role these bacterial communities play in uterine health and fertility.
• Research should explore how dynamic changes in the microbiome relate to immune responses and reproductive outcomes.
• Longitudinal studies following individual mares over several cycles could clarify temporal microbiome changes.
• Potential development of microbiome-targeted interventions to support equine reproductive health.