Multi-omics analysis reveals seasonal variation in ovarian lipid metabolism associated with vitamin D3 in the muskrats

Seasonal reproduction is critical for animals adapting to environmental changes, yet the mechanisms driving these shifts remain incompletely understood. Gut microbiota are increasingly recognized as important modulators of reproductive health, but their roles in seasonal breeding species remain unclear. In the muskrat (Ondatra zibethicus), a well-established seasonal breeder, morphological and histological analyses revealed enhanced follicular development during the breeding season (BS). Subsequent integrated ovarian transcriptomics and metabolomics identified that lipid metabolic processes were significantly enriched during the BS. This was validated by the increased expression of key lipid metabolic enzymes (e.g., DGAT1, CPT1A) and elevated triglyceride content in BS ovaries. Systemically, we found that serum vitamin D3 (VD3) and ovarian vitamin D receptor (VDR) expression were significantly elevated during BS. In contrast, analysis of upstream factors during the non-breeding season (NBS) showed a significant enrichment of gut Lactobacillus and a concurrent elevation of plasma lithocholic acid (LCA), a known VDR agonist. Correlation analyses confirmed that both Lactobacillus and LCA were inversely associated with serum VD3 levels. Critically, in vitro experiments demonstrated that VD3 treatment enhanced the expression of key lipid metabolism genes in muskrat granulosa cells. Collectively, our findings provide evidence for a gut microbiota-VD3-ovary axis that modulates seasonal ovarian lipid metabolism and function. This axis represents a new layer of host-microbiota interaction in reproductive physiology.