Compositional and Functional Metabolic Shifts in the Endometrial Microbiota of Cows (Bos taurus) During the Transition Period: A Metagenomic Next-Generation Sequencing Approach

Background: Significant alterations in feeding, housing, and physiology are observed in dairy cows during the transition period (3 weeks pre- and post-calving), in addition to changes in the composition and abundance of the endometrial microbiota. Thus, this study aimed to evaluate any changes in the composition and predicted metabolic pathways in the cow uterine microbiome during this transition period. Methods: Scrapings were sampled from the endometrial surface of clinically healthy cows (n = 3) in dynamics as follows: in the 10 Days period before, and on Days 3, 5, and 20 after calving. Total DNA was isolated from the samples, and the composition of the microbial community was assessed using targeted next-generation sequencing (NGS) technology. Based on the subsequent NGS data, the dynamics of the predicted metabolic pathways of the microbiota were evaluated. Results: Seven superphyla and phyla of microorganisms were found in the endometrial microbiota of cows during the transition period. Among these, the phylum Firmicutes (with a dominant class of Clostridia) and the superphylum Fusobacteriota (represented by a single class of Fusobacteriia) can be considered the dominant bacteria in the endometrium, with representation noted from 25.2 to 68.2% and from 12.3 to 51.1%, respectively. The microbiome composition underwent significant changes (p < 0.05) during the transition period. In particular, the high abundance of the Fusobacteriaceae family (up to 68.2%) in the uterus of clinically healthy cows was unexpected, given the potential association of Fusobacteriaceae with the occurrence of metritis in cows. The numbers of microorganisms in two dominant classes, Fusobacteriia and Clostridia, showed generally opposite changes in their relative abundance during the transition period. The predicted functional potential level for 32 pathways in the endometrium changed (p < 0.05) in cows during the transition period. Indeed, the activity of the predicted pathways, such as pyridoxal 5′-phosphate biosynthesis I and teichoic acid (poly-glycerol) biosynthesis, was lowered on day 3 postpartum (p < 0.05). Conclusions: Microbiota composition and the activity of the predicted metabolic pathways in the cow endometrium underwent significant changes at different critical stages in the transition period. Moreover, even clinically healthy cows exhibited signs of dysbiotic disorders.