Fermentation quality, bacterial community, and predicted functional profiles in silage prepared with alfalfa, perennial ryegrass and their mixture in the karst region

Abstract

There is little information regarding the dynamics of fermentation products and the bacterial community in silage prepared with alfalfa (MS), perennial ryegrass (LP), and their mixture in the karst region. In this study, we explored the effects of combining MS with LP in different ratios (100% MS, 70% MS + 30% LP, 50% MS + 50% LP, 30% MS + 70% LP and 100% LP; fresh matter basis) on silage chemical composition, fermentation quality, bacterial communities and predicted functions during the ensiling process. Each treatment was prepared in triplicate and stored at room temperature (22–25°C) for 7, 15, and 45 days. The dry matter (DM) and water-soluble carbohydrate content of the silages increased as the LP proportion in the mixed silage increased; at 45 days, the 70% MS + 30% LP, 50% MS + 50% LP and 30% MS + 70% LP silages contained higher (p < 0.05) CP content than the 100% MS and 100% LP silages. The 30% MS + 70% LP and 100% LP silages exhibited lower (p < 0.05) pH and higher (p < 0.05) LA content than the other silages; at 45 days, none of the silages contained PA or BA. As fermentation proceeded, the abundance of harmful (Enterobacteriaceae and Sphingomonas) and beneficial (Lentilactobacillus, Lactiplantibacillus, Secundilactobacillus, and Levilactobacillus) microorganisms decreased and increased, respectively, as the LP proportion in the mixed silage increased. The predicted functional distribution of microbial communities and metabolic pathways revealed that the 30% MS + 70% LP and 100% LP silages had a stronger capacity for fermentation and a weaker capacity for nitrate reduction than the other silages. Moreover, as the fermentation proceeded, the 30% MS + 70% LP and 100% LP treatments enhanced the functions of “Metabolism,” “Genetic information processing” and “Organismal systems” at level 1, the functions of “Amino acid metabolism” and “Nucleotide metabolism” at level 2, and the functions of “Metabolic pathways,” “Biosynthesis of secondary metabolites,” “Biosynthesis of antibiotics” and “Purine metabolism” at level 3. Thus, adding LP could improve the fermentation quality of MS silage by changing the composition and metabolic function of microbes; furthermore, ensiling 30% alfalfa with 70% ryegrass can produce high-quality silage in the karst region.

Lactic Acid Bacteria and Formic Acid Improve Fermentation Quality and Beneficial Predicted Functional Characteristics in Mixed Silage Consisting of Alfalfa and Perennial Ryegrass

“…The metabolic pathways were specifically analyzed at the third level. The relative abundances of "biosynthesis of secondary metabolites" and "biosynthesis of antibiotics" in the FA and LAB groups were greater than those in the CK group after 7 and 45 days of ensiling, and similar results were found in the study of Fan et al [14]. The relative abundances of "ABC transporters" in the FA group after 7 days of ensiling and in the FA and LAB groups after 45 days of ensiling were lower than those in the CK group.…”

“…Consequently, ensiling AL with PR might be a useful technique for enhancing the nutritional value and fermentation quality of silage. However, even though our previous studies showed that the nutritional quality of mixed silage ensiled with AL and PR improved, the fermentation quality was not satisfactory (pH 4.63-5.94) [14]. Hence, according to previous studies, silage additives are required to further improve the fermentation quality of mixed silage ensiled with AL and PR.…”

“…The numbers of epiphytic lactic acid bacteria, yeasts, and coliform bacteria on the fresh PR were 4.47, 2.63, and <2.00 log 10 CFU/g FW, respectively. AL was mixed with PR at a ratio of 3:7 on an FM basis, as this ratio resulted in relatively favorable fermentation quality in the mixed silage in our previous experiments [14]. Approximately 300 g of chopped forage was evenly mixed at a previous ratio of 3:7, and manually loaded into polyethylene bags (25 cm × 30 cm); then, a vacuum-packaging machine (SJ-400, Shanghai Precision Machinery Manufacturing Co., Ltd., Shanghai, China) was used for vacuum-packaging.…”

Ensiling hybrid Pennisetum with lactic acid bacteria or organic acids improved the fermentation quality and bacterial community

“…Generally, NH 3 -N accumulates continuously during fermentation ( Dong et al, 2022a ). When LAB dominated in the late stages of ensiling, lactic acid was produced by the fermentation of plant biomass and the pH was reduced to a level that inhibited the activity of ammonia nitrogen producing bacteria ( Fan et al, 2022 ). This could explain the correlation between pH and the NH 3 -N:TN ratio.…”

The Effect of Lactobacillus planturum YQM48 Inoculation on the Quality and Microbial Community Structure of Alfalfa Silage Cultured in Saline-Alkali Soil

“…The decrease in DM and carbohydrates is due to the metabolic activity of lactobacilli during fermentation. These microorganisms convert nutrients into organic acids, ethanol, and other metabolic products [21,22].…”