Combining the Vaginal Microbiome and Serum Metabolome to Screen for Potential Biomarkers of Early Pregnancy in Cows

Early pregnancy diagnostic techniques are of significant importance in livestock farming, particularly in dairy farming. This study aimed to screen artificially inseminated cows for potential biomarkers at day 21 of pregnancy using microbiota–metabolomics analysis. The microbiome analysis revealed significant changes (p < 0.05) in the composition and abundance of the vaginal microbiota in cows after pregnancy. Notably, there was an increase in the abundance of [Eubacterium]_hallii_group (p < 0.05) associated with the production of short-chain fatty acids in the pregnant group compared with the non-pregnant group. Furthermore, significant alterations were observed in the serum metabolome, with notable changes in the concentrations of prolyl-hydroxyproline (Pro-Hyp) (p < 0.01) and bonactin (p < 0.01). The majority of differential metabolites clustered within the pathways of amino acid metabolism and lipid metabolism, with lipid metabolism exhibiting a higher proportion and playing a pivotal role in early pregnancy. An enzyme-linked immunosorbent assay was employed to quantify three key metabolites of the arachidonic acid pathway. The results demonstrated significant decreases in serum concentrations of leukotriene B4 (LTB4) (p < 0.05) and prostaglandin F2α (PGF2α) (p < 0.01) and no significant changes in arachidonic acid (AA) (NS) concentrations after 21 days of gestation in cows. Spearman’s correlation analysis was utilized to investigate the interrelationship between the vaginal microbiota and serum metabolites. In conclusion, the present study demonstrated that biomaterials such as bonactin, Pro-hyp, LTB4, PGF2α in serum metabolites and [Eubacterium]_hallii_group in the vaginal flora of cows could be utilized as potential biomarkers for 21 days of gestation in cows.