Semen Microbiome Influence on the Mare Uterine Microbiome - e-coli bacteria, a common equine uterine bacteriaSemen Microbiome Influence on the Mare Uterine Microbiome

While semen-uterine microbiome interactions have been described in humans, equivalent data in horses was absent. Using a cross-species insemination model, this study investigated whether the male seminal microbiome influences the mare uterine microbiome and whether post-breeding microbiome composition affects embryo recovery.

Study Design:

  • 22 fertile mares inseminated with raw semen (2 billion sperm) from either a donkey jack or horse stallion in a cross-over design with washout cycle between treatments
  • Uterine fluid sampled before insemination, at 6 hours, 24 hours, and 8 days post-ovulation at embryo flush
  • Bacterial DNA sequenced via full-length 16S region; taxonomic analysis performed to family level

Key Results:

  • Semen microbial diversity differed significantly between donkey and horse (p=0.048)
  • Dominant phyla in both groups: Proteobacteria, Actinobacteria, and Firmicutes — proportions differed between species
  • Lactobacillales contributed up to 20% of uterine microbiome in donkey-bred mares versus 6% in horse-bred mares
  • 24 bacterial families shared between donkey semen and post-insemination uterine microbiome; 9 shared between horse semen and uterine microbiome
  • Uterine microbiome composition at 8 days post-ovulation differed significantly based on embryo recovery outcome (p=0.02)

Conclusions:

  • Semen microbiome composition demonstrably influences the mare uterine microbiome post-breeding
  • A temporary combined male-female microbiome appears to have measurable consequences for embryonic recovery
  • First demonstration in horses of a semen-to-uterus microbiome transfer effect

(Podico G, Canisso IF. 2025. The semen microbiome influences the mare uterine microbiome. Journal of Equine Veterinary Science 145:105314. https://doi.org/10.1016/j.jevs.2024.105314)