Effect of storage time on the fermentation quality, bacterial community structure and metabolic profiles of napiergrass (Pennisetum purpureum Schum.) silage

This study was aimed to investigate the effect of storage time on fermentation characteristics, bacterial community structure and predicted metabolic pathways of napiergrass (Pennisetum purpureum Schum.) silage. First-cutting napiergrass was harvested at the vegetative stage and ensiled in laboratory-scale silos (1 L capacity). Triplicate silos were sampled after 1, 3, 7, 15, 30 and 60 days of ensiling, respectively. The bacterial communities on day 3 and 60 were assessed through the high throughput sequencing technology, and metabolic pathways of bacterial community were predicted according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) via Tax4Fun. Napiergrass silage exhibited an acetic acid-type fermentation, indicated by lower lactic acid contents and ratio of lactic acid to acetic acid, and higher pH, ethanol and acetic acid contents. Before ensiling, the predominant genera in fresh napiergrass mainly included Acinetobacter, Enterobacteriaceae, Enterobacter and Lactococcus. After 60 days of ensiling, high proportions of Enterobacteriaceae, Enterobacter and Lactobacillus were found in napiergrass silages. The metabolism of amino acid, energy, cofactors and vitamins were inhibited, whereas metabolism of nucleotide and carbohydrate were promoted during ensiling. Overall, the combination of high throughput sequencing technology and 16S rRNA gene-predicted functional analyses revealed the differences during the initial and late stages of napiergrass silages not only for distinct bacterial community but also for specific functional metabolites. It could provide a comprehensive insight into bacterial community and functional profiles to further improve the silage quality.