Dynamics of fermentation profile and bacterial community of silage prepared with alfalfa, whole-plant corn and their mixture

Abstract

Silage fermentation improves when alfalfa is ensiled along with whole-plant corn, yet so far the impact of their mixing ratios on individual bacteria during fermentation is weakly described. The objective of this work was to explore the effect of combining alfalfa with whole-plant corn in different ratios on silage bacterial community and fermentation profile over the entire ensiling process. The alfalfa at the early bloom stage and whole-plant corn at around the 1/3 milk line stage were freshly chopped and blended at proportions of 1:0 (served as Control), 0.8:0.2 (Mix 1), 0.6:0.4 (Mix 2) and 0:1 on a fresh matter basis. Each treatment was prepared in triplicate and ensiled in plastic bag silos for 0, 3, 7, 14 and 35 days. The fermentation coefficient of fresh matter used to asses a forage ensilability linearly increased, with more corn in the mixture. During the first 3 days of fermentation, the greatest pH drop occurred in all silages. Seven days later, the silage pH in Mix 1, Mix 2 and corn further decreased, and alfalfa silage pH slightly increased, however. After 35 days of ensiling, alfalfa silage was poorly fermented, shown by a high level of pH (4.69), acetic acid (35.7 g/kg dry matter), propionic acid (29.0 g/kg dry matter), n-butyric acid (12.1 g/kg dry matter) and ammonia nitrogen (108 g/kg total nitrogen). Silage fermentation was significantly improved with corn percentage increasing from 20 % to 100 %. In the early stage of fermentation, Lactobacillus and Pediococcus relative abundance noticeably increased in alfalfa, Mix 1 and Mix 2 silages, whereas Leuconostoc abundance was noticeably enriched and outnumbered Lactobacillus and Pediococcus in corn silage. During 7–35 days of ensiling, the bacterial community structure in all silages comparatively stayed stable. Besides, Lactobacillus abundance increased while Pediococcus and Weissella richness decreased with more corn, at each period above. The bacterial community composition of all fresh materials was similar at the genus level, consisting mainly of Weissella, Leuconostoc, Pantoea, Enterobacter, Pseudomonas and Rosenbergiella. However, the development of Lactobacillus, Pediococcus and Leuconostoc species in alfalfa, Mix 1 and Mix 2 silages in the early stage of fermentation was different from corn silage. Subsequently, the bacterial community structure in all silages relatively stayed stable. Overall silage fermentation quality was better when alfalfa was ensiled in a mixture with at least 20 % whole-plant corn on a fresh matter basis.