Abstract
The aim of this study was to investigate effects of wilting and Lactobacillus plantarum inoculation on the dynamics of the fermentation products, residual non-structural carbohydrates, and bacterial communities in alfalfa silage. Fresh and wilted alfalfa were ensiled with and without L. plantarum for 10, 30, 60, and 90 days. A high-throughput sequencing method for absolute quantification of 16S rRNA was adopted to determine the bacterial community composition at different ensiling periods. For the wilted silage, the bacterial community, pH value, and ammonia nitrogen concentration remained stable in the silage at 30 days. L. plantarum inoculation accelerated lactic acid fermentation and altered the predominant genus in the wilted silage as compared with the non-inoculated group. For the non-wilted group, fast consumption of water-soluble carbohydrates (WSCs) was observed at 10 days in the non-inoculated silage along with rapid growth of undesirable Hafnia. L. plantarum inoculation inhibited growth of Hafnia at 10 days in the non-wilted silage. Clostridia fermentation occurred in the non-wilted silage at 90 days, as indicated by an increased pH, formation of butyric acid (BA), and apparent abundance of genera belonging to Clostridia. L. plantarum inoculation inhibited BA accumulation and growth of Garciella in the non-wilted silage at 90 days as compared with the non-wilted silage without inoculation, but had little effect on the growth of Clostridium sensu stricto. Overall, the high moisture content of the non-wilted alfalfa silage led to rapid consumption of WSCs and growth of harmful microorganisms at the early stage of ensiling, resulting in poor fermentation quality. Wilting and L. plantarum inoculation both improved fermentation quality and inhibited the growth of spoilage microorganisms in alfalfa silage, while L. plantarum inoculation alone failed to achieve optimum fermentation quality of non-wilted alfalfa silage.
Highlights
Year-round access to good quality silage is essential for ruminants
The objective of this study is to investigate effects of wilting on the dynamics of fermentation products, residuals of non-structural carbohydrates, and bacterial communities in alfalfa silage with and without L. plantarum inoculation
For each treatment, 12 kg of alfalfa was randomly divided into 24 equal parts (500 g each) and packed into polyethylene plastic bags, which were vacuum sealed with a Shineye P290 Vacuum Packaging Sealer (Dongguan Yijian Packaging Machinery Co., Ltd., Dongguan, China)
Summary
Year-round access to good quality silage is essential for ruminants. As forage production is seasonal in many areas, ensiling is used globally for forage preservation, especially during rainy seasons (Eikmeyer et al, 2013). The competition of LAB against other microorganisms is affected by multiple factors, including moisture content, aerobic conditions, and composition of epiphytic microorganisms in fresh forage (Eikmeyer et al, 2013; Kasmaei et al, 2017; Wang et al, 2019). Lactobacillus plantarum is the most commonly used bacterial inoculant in forage ensiling studies (Oliveira et al, 2017) and is widely applied in alfalfa silage production. Previous studies have reported an increased risk of Clostridia fermentation when the moisture content of the alfalfa silage exceeds 70% (Coblentz and Muck, 2012; Yang et al, 2020). Previous studies reported that wilting of wet alfalfa material before ensiling could improve the fermentation quality of the silage (Tao et al, 2017; Agarussi et al, 2019). The abundance of epiphytic microbes might be altered along with the consumption of WSCs during wilting
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