Metagenomic analysis of the vaginal microbiota in cows with ovarian cysts

Abstract Introduction This study compared the vaginal microbiota composition of dairy cows with follicular and luteal ovarian cysts using metagenomic analysis. Material and Methods Ovarian cysts, which impair reproductive performance through endocrine disruption, were diagnosed by ultrasonography and serum hormone evaluation in Holstein cows 30–60 d postpartum. Forty-five cows were initially included and divided into follicular cyst, luteal cyst and control groups. Vaginal lavage samples were analysed using third-generation sequencing, and taxonomic classification was performed through 16S rRNA gene analysis. Results A total of 258 operational taxonomic units (OTUs) were identified, with the highest diversity observed in the control group (mean of 56.8 OTUs) and the lowest in the luteal cyst group (mean of 49.0 OTUs). Proteobacteria was the dominant phylum across all groups (93.4%), followed by Tenericutes (5.9%). Firmicutes, Bacteroidetes and Fusobacteria accounted for less than 1%. At the family level, Burkholderiaceae (62.7%) and Pasteurellaceae (24.0%) were predominant, while of the genera, Ralstonia was the most abundant (62.2%). The luteal group had the highest relative abundance of Burkholderiaceae, whereas Pasteurellaceae was most abundant in the control group. Conclusion These results indicate that cystic cows exhibit reduced microbial diversity and altered bacterial composition in comparison with healthy animals. The predominance of Proteobacteria and Ralstonia suggests a potential link between endocrine imbalance and changes in the vaginal microenvironment. Hormonal analyses supported the classification of cyst types, with follicular cyst cows showing low progesterone (0.31 ± 0.05 ng/mL) and high oestradiol-17β concentrations (55.57 ± 7.91 pg/mL), whereas luteal cyst cows exhibited higher progesterone (2.89 ± 0.74 ng/mL) and lower oestradiol-17β concentrations (6.19 ± 0.56 pg/mL) (P < 0.001). These results may support future studies evaluating vaginal microbial profiles as complementary indicators of ovarian status in dairy cows.