Characterization of bacterial community and fermentation parameters during ensiling of Napier grasses harvested at various times within a day

Abstract

Grasses exhibit variations in chemical composition and epiphytic microbiota during daylight. These variations may influence the natural fermentation parameters of silage. This study was to evaluate the bacterial community and fermentation parameters during ensiling of Napier grasses harvested at various times within a day. Secondary growth of Napier grass (vegetative stage) was harvested at 7:00 (AM), 12:00 (M) and 17:00 (PM) on three sunny days. The Napier grasses were ensiled in polyethylene plastic bags and bags were opened after 1, 3, 7, 14, 30 and 60 days. Compared with AM-cut fresh Napier grasses, M and PM-cut fresh Napier grasses had higher (P < 0.05) dry matter, and lower (P < 0.05) crude protein contents and buffering capacity. The lactic acid bacteria (LAB) and aerobic bacteria counts decreased (P < 0.05) with the delay of harvest time. Compared with AM silage, M and PM silages exhibited slower pH declines and WSC consumptions plus less lactic acid production during ensiling. After 7 days of ensiling, propionic acid contents and DM losses tended to be higher (P < 0.05) in M and PM silages compared with AM silage. The M and PM-cut fresh Napier grasses had higher (P < 0.05) bacterial diversity and richness than AM-cut fresh Napier grasses. During ensiling, Lactobacillus gradually dominated the microbiota in AM silage and its relative abundance reached 49.1% at the end of ensiling. By contrast, Klebsiella and Enterobacter tended to flourish in the M and PM silages as ensiling progressed. Analysis of the LAB community showed that M and PM-cut fresh Napier grasses had higher (P < 0.05) relative abundance of Leuconostoc and lower (P < 0.05) Lactococcus compared with AM-cut fresh Napier grasses. On day 3 of ensiling, the relative abundance of Leuconostoc and unclassified_f_Leuconostocaceae were higher (P < 0.05), and Lactococcus and unclassified_o_Lactobacillale were lower (P < 0.05) in M and PM silages as opposed to those in AM silage. After 14 days of ensiling, M and PM silages contained higher Pediococcus and Enterococcus compared with AM silage. These results revealed that Napier grasses harvested at various times within a day had different fermentation parameters and bacterial community during ensiling. In practice, diurnal changes in Napier grass could be an important factor to consider for producing high-quality silage.