An evaluation of storage length on ensiling characteristics, bacterial community compositions, co-occurrence networks, and their functional shifts and pathogenic risk in high-moisture oat silage

This study aimed to evaluate the ensiling characteristics, bacterial community structure, co-occurrence networks, and their predicted functionality and pathogenic risk in high-moisture oat (Avena sativa L.) silage. The oat harvested at heading stage (224 g/kg fresh weight) was spontaneously ensiled in plastic silos (10 L scale). Triplicate silos were opened after 1, 3, 7, 15, 30 and 60 days of fermentation, respectively. The bacterial community structure on day 3 and 60 were investigated using high-throughput sequencing technology, and 16S rRNA-gene predicted functionality and phenotypes were determined by PICRUSt2 and BugBase tools, respectively. After 60 days, the oat silage exhibited moderate fermentation quality, as indicated by large amounts of acetic acid (~ 50.4 g/kg dry matter (DM)) and lactic acid (~ 55.4 g/kg DM), relatively high pH (~ 4.79), acceptable levels of ammonia nitrogen (~ 75.2 g/kg total nitrogen) and trace amounts of butyric acid (~ 3.36 g/kg DM). Psychrobacter was prevalent in fresh oat, and Enterobacteriaceae and Lactobacillus dominated the bacterial community on day 3 and 60. Ensilage reduced the complexity of bacterial community network at the initial stage of fermentation. The bacterial functional pathways in fresh and ensiled oat are primarily characterized by the metabolism of carbohydrate and amino acid. During ensiling, the elevated pyruvate kinase and 1-phosphofructokinase levels were correlated with the lactic acid production, and the increased levels of 6-phosphogluconate dehydrogenase and ribulose-5-phosphate 3-epimerase may be responsible for the abundant acetic acid contents. Greater (P < 0.01) proportions of “Potentially Pathogenic” were observed in the bacterial community of oat silage compared to fresh oat. Altogether, the findings indicated that the high-moisture oat silage exhibited moderate fermentation quality, and the potential for microbial contamination and pathogens remained after 60 days of ensiling. Therefore, some effective chemical and microbial additives are recommended to ensure the quality, hygiene, and safety in high-moisture oat silage production.