Table_1_Potential factors causing failure of whole plant nettle (Urtica cannabina) silages.xlsx

IntroductionNettle is kind of new feed resources and benefit for animal production. However, a few studies observed that quality of nettle silage was poor under naturally fermentation. Consider of microbial activity was the mainly factors for fermentation characteristics of silage.
MethodsThus, the present study investigated the potential factors causing nettle silage failure through metabolome and bacterial community composition analyses during ensiling.
ResultsDuring ensiling, the pH was >6.22, and water-soluble carbohydrate and organic acid contents stabilized after 7 d. At the genus level, Enterococcus, Weissella, and Pediococcus were the dominant bacteria (relative abundance were 30.06–39.39, 17.29–23.34, and 3.13–7.22%, respectively), with stable trends, whereas Lactococcus and Enterobacter relative abundance decreased significantly over time (relative abundance were 5.68–13.96 and 3.86–24.1%, respectively). Lactobacillus relative abundance was <1% during the entire ensiling period, and malic acid metabolic pathway was the most important pathway. Enterococcus, Pediococcus, and Weissella were negatively correlated with malic acid, with Lactobacillus displaying an opposite trend.
DiscussionThe results suggested that Lactobacillus activity was the lowest among lactic acid bacteria (LAB) during ensiling, which is the main reason for nettle ensiling failure, and attributable to a low capacity to compete for fermentation substrates such as malic acid against other LAB during ensiling. Additionally, anti-bacteria activity of nettle probably inhibited Enterobacter activity during ensiling. Present study probably given a solution for improve nettle silage quality through addition with malic acid.

引言
荨麻是一种新型饲料资源，对动物生产具有积极效益。然而，已有少量研究发现，自然发酵条件下荨麻青贮饲料的品质较差。鉴于微生物活性是影响青贮饲料发酵特性的主要因素。
方法
为此，本研究通过代谢组学分析与青贮发酵过程中的细菌群落组成解析，探究引发荨麻青贮发酵失败的潜在诱因。
结果
青贮发酵过程中，发酵液pH值始终高于6.22，水溶性碳水化合物与有机酸含量在发酵7天后趋于稳定。在菌属水平上，肠球菌属（Enterococcus）、魏斯氏菌属（Weissella）与片球菌属（Pediococcus）为优势菌群，相对丰度分别为30.06%~39.39%、17.29%~23.34%及3.13%~7.22%，其相对丰度呈现稳定趋势；而乳球菌属（Lactococcus）与肠杆菌属（Enterobacter）的相对丰度随发酵时间显著降低，对应相对丰度范围分别为5.68%~13.96%与3.86%~24.1%。整个青贮发酵周期内，乳杆菌属（Lactobacillus）的相对丰度均低于1%，而苹果酸代谢通路为最关键的代谢通路。肠球菌属、片球菌属与魏斯氏菌属与苹果酸呈负相关关系，乳杆菌属则呈现相反的变化趋势。
讨论
本研究结果表明，在青贮发酵过程中，乳杆菌属（Lactobacillus）在乳酸菌（Lactic Acid Bacteria，简称LAB）中的活性最低，这是荨麻青贮发酵失败的主要原因，其根源在于相较于其他乳酸菌，乳杆菌属在竞争苹果酸等发酵底物时能力较弱。此外，荨麻本身的抗菌活性可能在青贮发酵过程中抑制了肠杆菌属的活性。本研究或可为通过添加苹果酸以提升荨麻青贮饲料品质提供可行解决方案。