Characterization of the cervical bacterial community in dairy cows with metritis and during different physiological phases

For the development of disease prevention and intervention strategies, a better understanding of the dynamics and interactions within cervical bacterial communities in both healthy cows and cows with metritis is required. Understanding the complexity and ecology of microorganisms in the vagina of dairy cows with metritis and during different physiological phases is critical for developing strategies to balance microorganism content. To gain deeper insight into fluctuations within the cervical microbiota, swab samples were collected from 40 Holstein dairy cows, and16S rDNA amplicon sequencing was used to analyze cervical bacterial diversity. Meanwhile, vaginal bacterial composition was analyzed during different physiological phases, including the formative (CF), gestational (CG), and postpartum (CP) stages, and in cows with metritis (CM). The results revealed a complex profile with extensive differences in the cervical bacterial composition. A total of 678,043clean 16S rDNA V4-V6 reads were gained, and 1877 Operational Taxonomic Units (OTUs) were observed after calculation. At both the phylum and genus levels, the top 10 bacteria by percentage were the same when comparing the CF, CG, and CP groups of cows, with some variation in abundance. At the phylum level, the cervical microbial community in the CF, CG, and CP groups included mainly Firmicutes, which accounted for 39.3%, 48.3%, and 49.6% of the total microbial composition of each group, respectively. However, the cervical bacterial community in the CM group consisted of mostly Bacteroidetes, which accounted for 72.6% of the total microbial composition. The second major bacterial community in the CF and CG groups of cows was Proteobacteria, which accounted for 28.3%and 30.1% of the total microbial compositions of these groups, respectively, while the second major bacterial community in the CP group was Bacteroidetes (23.5%). However, in the CM group, the second major bacterial community was Fusobacteria, which accounted for18.0% of the total microbial composition. At the genus level, the cervical bacterial community in the CM group of cows was dominated by Porphyromonas(44.4%) and Fusobacterium(12.1%), while Porphyromonas accounted for only 1.3%, 1.1%, and 1.4% of the total microbial compositions of the CF, CG, and CP groups, respectively. Likewise, Fusobacterium accounted for 2.3%, 0.7%, and 4.7% of the total microbial compositions of the CF, CG, and CP groups, respectively. The results demonstrate that cervical bacterial diversity decreases in cows with metritis and that the predominant bacterial genera are Porphyromonas and Fusobacterium. Cervical bacterial diversity was rich in all observed physiological phases, and the predominant bacterial phylum was Firmicutes. Pregnancy had little effect on the cervical bacterial community; however, there were increases in the abundances of pathogenic species in postpartum cows. Cervical bacterial diversity decreased in cows with metritis, however, due to the highly dynamic and complex course of metritis, the relationship between cervical bacterial diversity and metritis requires further investigation.