Shotgun metagenomic composition, microbial interactions and functional insights into the uterine microbiome of postpartum dairy cows with clinical and subclinical endometritis

Clinical endometritis (CE) is associated with bacterial pathogens while the same has not been proved about subclinical endometritis (SCE). We aimed to use shotgun metagenomic sequencing to investigate the associations between potentially unidentified pathogens and SCE. Uterine cytobrush samples from multiparous Holstein cows (n = 23) were taken at 21 days in milk (DIM) and sequenced via the Illumina shotgun platform. At 36 DIM, the cows were diagnosed as CE (n = 7), SCE (n = 7), or healthy (n = 9). We did not find differences in the alpha and beta diversity of bacteria and eukaryotes among the health groups. Relative abundance of typical pathogens i.e. Fusobacterium, Peptoniphilus, Peptostreptococcus, and Trueperella was greater in CE than healthy controls. We did not find evidence of eukaryotic or viral association in infection, yet, distinct patterns of bacterial co-occurrence were observed among pathogenic and non-pathogenic bacteria. In CE cows, Wnt/catenin pathway had lower abundance than SCE or healthy cows. Our findings support that CE is characterized by domination of pathogenic bacteria that intercorrelate, whereas SCE is not associated with bacterial colonization.