The characteristics of diarrhea-related bacteria in suckling calves and their dynamic succession with ages

Background Calf diarrhea is one of the major health problems in calf rearing on dairy farms worldwide. The gut microbes have great influence on prevention and treatment of calf diarrhea, but their role in diarrhea is still lacking. The objective of this study was to identify the diarrhea-related bacteria in two different days of age, and to investigate whether these bacteria were affected by calf ages. Results Forty-eight new-born female calves were selected for recording the fecal score daily and collecting the rectal content at 15 and 35 days of age, respectively. The diarrhea status and health score of calves in two different ages were evaluated according to the fecal score. The rectal microbial fermentation and microbial community structure were different between high-health-status calves and low-health-status calves. Compared to calves with high health status, the low-health-status calves had decreased butyrate molar proportion in rectal feces at both 15 days of age and 35 days of age (P < 0.05). The LEfSe analysis showed that the relative abundance of Butyricicoccaceae (Butyricicoccus) and Clostridiaceae (such as Clostridium sensu stricto 1 and Clostridium perfringens) were higher in low-health-status calves at both 15 days of age and 35 days of age. However, the relative abundance of Bifidobacterium, Streptococcus, and Peptostreptococcus were lower in low-health-status calves at 15 days of age. At 35 days of age, we found that some member in Prevotellaceae (such as Prevotellaceae bacterium and Prevotella) were especially decreased in low-health-status calves. Using random forest regression analysis, most of these genera mentioned above were identified as diarrhea-related bacteria. Furthermore, we have further revealed that some bacteria, like Erysipelotrichaceae_UCG-003 and Mogibacterium, were additional diarrhea-related bacteria at 15 days of age. While other bacteria, including Megasphaera, Prevotella 9, Romboutsia, and Citrobacter were additional diarrhea-related bacteria at 35 days of age. The microbial co-occurrence network analysis revealed that the interaction patterns of calf microbiome changed with diarrhea status and ages. Particularly, the potential pathogens, like Escherichia Shigella, had increased participation in co-occurrence networks of diarrheic calves. Among these diarrhea-related bacteria, the genera that positively correlated with health score had apparent co-exclusion with the genera that negatively correlated with health score, but they correlated with rectal short chain fatty acids positively. Conclusions Overall, our study revealed that the diarrhea-related bacteria of calves will vary at different ages, which may contribute to the treatment and prevention of diarrhea in the calf industry by targeted microbial intervention.