Unraveling the relationship between the vaginal microbiome and return to estrus in post-weaning sows

BACKGROUND: Return to estrus in post-weaning sows has a significant impact on reproduction performance. Changes in sex hormone levels influence the composition of the vaginal microbiota in sows. However, the relationship between return to estrus and the vaginal microbiota in post-weaning sows remains poorly understood. RESULTS: In this study, we characterized the vaginal microbiota of 74 Landrace × Yorkshire post-weaning sows including 40 normal-return and 34 non-return sows by sequencing the V3-V4 region of the 16 S rRNA gene. The results revealed significant differences in both the composition and predicted functional capacities of the vaginal microbiota between normal-return and non-return sows. Non-return sows were characterized by reduced abundances of Clostridium sensu stricto 1, Lactobacillus, and Christensenellaceae R-7 group, and increased abundances of Facklamia and Weissella. Furthermore, the predicted functional pathways of Clostridium acetobutylicum acidogenic fermentation and pyruvate fermentation to butanoate were significantly enriched in normal-return sows. Significant differences were also observed in the co-occurrence networks of the vaginal microbiota between normal and non-return sows, revealing distinct microbial interaction patterns between normal return and non-return sows. A random forest analysis identified several vaginal bacterial taxa that showed high discriminatory capacity between normal and non-return sows (AUC = 0.907), including Rikenellaceae RC9 gut group and Christensenellaceae R-7 group that were strongly associated with return to estrus in post-weaning sows. CONCLUSIONS: We observed significant differences in the composition and predicted functional capacities of the vaginal microbiota between normal-return and non-return sows, and identified several bacterial taxa associated with return to estrus of weaned sows. These findings enhance our understanding of the relationship between the vaginal microbiota and return to estrus in post-weaning sows and provide a foundation for future mechanistic and interventional studies.