Effects of Intra-uterine Ceftiofur on the Equine Uterine Microbiome

Antimicrobial therapy is a mainstay for treating reproductive diseases, including endometritis. Ceftiofur, a third-generation cephalosporin, is a common antibiotic used to treat equine bacterial endometritis. It is also routinely given empirically as an intra-uterine (IU) infusion in broodmare practice. We hypothesized that ceftiofur IU would disrupt the resident microbial community within the healthy uterus of mares. To test our hypothesis, eight university-owned mares were selected for characterization of the estrual uterine microbiome before and after IU ceftiofur. Double-guarded swabs of the estrual endometrium were taken before and 3 days after both IU saline and ceftiofur in a crossover design. Isolation of DNA from endometrial swabs was performed, followed by amplification of the V4 region of the 16S rRNA gene by Illumina Miseq sequencing to examine core bacterial communities present before and after ceftiofur. The uterine microbial composition of sham and ceftiofur-treated mares was not significantly different as measured by beta diversity. The only notable difference was a lower abundance of Christensenellaceae_R-7_group after ceftiofur (0.14 ± 1.05% vs. 2.89 ± 1.07% control; <i>p</i> = 0.0428). In conclusion, three-day treatment of ceftiofur did not change the microbial composition acutely within the mare uterus when sampled directly after treatment. Ceftiofur may have a long-term effect on the uterine microbiome, which may require sampling several weeks post treatment. In conclusion, ceftiofur does not change the healthy uterine microbiome acutely during estrus and but should still be used judiciously.