Metagenomic characterization of the equine endometrial microbiome during anestrus.
Authors: Heil B A, van Heule M, Thompson S K, Kearns T A, Beckers K F, Oberhaus E L, King G, Daels P, Dini P, Sones J L
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Equine Endometrial Microbiome During Anestrus The equine uterus undergoes profound hormonal changes across the estrous cycle, yet research on the endometrial microbiome has focused almost exclusively on the estrous phase when mares are typically examined for breeding soundness. Heil and colleagues used 16S rRNA gene sequencing to characterise the bacterial communities in endometrial swabs collected from 16 mares during estrus and 8 of the same mares during the subsequent anestrous season, providing the first direct comparison of microbial composition across these reproductive states. Notably, the anestrous endometrium harboured significantly greater microbial diversity and richness than the estrous uterus, though both phases were dominated by the same three phyla—Proteobacteria, Firmicutes, and Bacteroidota—suggesting that hormonal fluctuations modulate the microbial landscape rather than fundamentally altering the core bacterial residents. The researchers propose that oestrogen-driven changes to the endometrial immune environment during estrus may suppress microbial diversity, though the functional consequences of these compositional shifts remain unclear. For practitioners involved in fertility management, this finding underscores that single endometrial samplings during estrus capture only one snapshot of the uterine microbiological milieu, and future work exploring whether anestrous dysbiosis predicts breeding complications or whether the seasonal shift in microbial structure reflects adaptive or pathological processes would strengthen clinical decision-making around endometritis diagnosis and treatment.
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Practical Takeaways
- •The uterine microbiome changes substantially with reproductive cycle stage, suggesting optimal breeding conditions may relate to specific microbial profiles during estrus
- •Understanding anestrus microbiome characteristics could inform management strategies for mares with subfertility or recurrent endometritis
- •Cycle-stage dependent microbiome differences should be considered when interpreting endometrial cultures or microbiome assessments for breeding soundness evaluation
Key Findings
- •Equine endometrial microbiome shows significantly higher diversity and richness during anestrus compared to estrus
- •Both estrus and anestrus microbiomes were dominated by Proteobacteria, Firmicutes, and Bacteroidota phyla
- •Microbial community composition differed significantly between anestrus and estrus stages
- •Differences in endometrial immune environment across the estrous cycle likely explain microbiome variation