Characterization of Blood Metabolites and the Uterine Microbiota in Estrus Simmental Cattle

Accurate oestrus detection is critical for optimizing reproductive efficiency in beef cattle, yet the underlying metabolic and microbial mechanisms remain poorly understood, particularly in Simmental cattle. To address this gap, we employed an integrated metabolomics and microbiome approach to systematically characterize blood metabolic profiles and uterine microbiota dynamics during oestrus. The results revealed significantly elevated serum levels of total protein, albumin, glucose and insulin-like growth factor-1 (IGF-1) (P<0.01) during oestrus, and metabolomics revealed 258 differentially abundant metabolites enriched primarily in amino acid and lipid metabolism pathways. Cervical microbiome analysis revealed Firmicutes and Bacteroidetes as the dominant bacterial phyla, whereas fungal Ascomycota presented significantly increased relative abundance (78.38% vs 67.20%) with reduced α diversity (P<0.05) during estrus. Functional prediction analysis further revealed significant enrichment of bacterial energy metabolism pathways (TCA cycle; q<0.01), strong positive correlations between Bacteroides and bile acids (r>0.6, P<0.01), and significant associations between Candida and lipid metabolites. These findings establish a 'microbiota‒metabolite‒host' interaction network specific to oestrus in Simmental cattle, providing novel theoretical foundations and potential biomarkers for optimizing reproductive management in cattle herds.