Effect of Ensiling Density and Storage Temperature on Fermentation Quality, Bacterial Community, and Nitrate Concentration of Sorghum-Sudangrass Silage

Abstract

This study aimed to evaluate the fermentation quality, bacterial community, and nitrate content of sorghum-sudangrass silage with two ensiling densities [550 kg fresh weight (FW)/m3 (low density, LD) and 650 kg FW/m3 (high density, HD)] stored at two temperatures [10°C (low temperature, LT) and 25°C (normal temperature, NT)] for 60 days. The fermentation parameters, microbial counts, bacterial community, nutritional composition, and nitrate and nitrite levels were assessed. The pH and ammonia nitrogen (N) in all silages were below 4.0 and 80 g/kg total N, respectively. Compared with LT treatments, NT treatments had lower pH and lactic acid (LA) bacteria and yeasts counts and contained higher LA and LA/acetic acid (LA/AA) (p < 0.05). The LT-LD contained more ammonia–N than LT-HD (p < 0.05) and had higher nitrate and lower nitrate degradation than other treatments (p < 0.05). Lactobacillus was the most dominant genus with all treatments (57.2–66.9%). The LA, LA/AA, and abundances of Pantoea, Pseudomonas, and Enterobacter in the silage negatively correlated with nitrate concentration and positively correlated with nitrate degradation (p < 0.05). Moreover, pH and ammonia–N were positively correlated with nitrate concentration and negatively correlated with nitrate degradation (p < 0.05). Overall, all silage had satisfactory fermentation quality, and the silage with HD and NT had better fermentation quality and higher nitrate degradation. The bacterial communities in all silages were dominated by Lactobacillus. The nitrate degradation during the fermentation process might be related to the fermentation quality and the activity of Pantoea, Pseudomonas, and Enterobacter in silage.

Effect of exogenous microorganisms on the fermentation quality, nitrate degradation and bacterial community of sorghum-sudangrass silage

“…The pH value of the extracts was determined using a pH meter (PB-10, Sartorius Group, Göttingen, Germany). Organic acids and nitrates were determined by high-performance liquid chromatography ( Bai C. et al, 2022 ). The concentrations of N 2 O in the gas samples were analysed by gas chromatograph (Agilent 7890A, Agilent Technologies Limited Co., United States) within a week ( Xu T. W. et al, 2017 ).…”

“…Previous studies have shown that microorganisms, such as Enterobacteriaceae and Lactobacillus, in silage forage can degrade nitrate (Spoelstra, 1985). Bai C. et al (2022) demonstrated that Panobacter spp., Pseudomonas spp., and Enterobacter spp. were negatively correlated with the nitrate content of silage sorghum-sudangrass.…”

“…Ensiling can reduce nitrate in sorghum-sudangrass to some extent content ( Spoelstra, 1987 ; Bai C. et al, 2022 ). During the ensiling process, nitrate is degraded to produce the intermediate product nitrite, and the end products nitric oxide, ammonia, and nitrous oxide ( Spoelstra, 1985 ).…”

“…During the ensiling process, nitrate is degraded to produce the intermediate product nitrite, and the end products nitric oxide, ammonia, and nitrous oxide ( Spoelstra, 1985 ). However, the nitrate content in silage may still threaten the health of ruminants by exceeding the safe limit of nitrate in forage ( Spoelstra, 1983 ; Bai C. et al, 2022 ). In response, researchers have tried to use silage additives to regulate the nitrate content in silage.…”

“…This methodology provides the possibility to deeply explain the nitrate degradation during silage. For example, Bai C. et al (2022) used high-throughput sequencing to illustrate the effects of Panobacter spp., Pseudomonas spp ., and Enterobacter spp. on the nitrate content of silage sorghum-sudangrass.…”