Effect of Mixing Peanut Vine on Fermentation Quality, Nitrogen Fraction and Microbial Community of High-Moisture Alfalfa Silage

Abstract

Fresh alfalfa is difficult to ensile successfully because of its high moisture content and greater susceptibility to spoilage by Clostridia, Bacilli or Enterobacter. In this study, we evaluated the effects of mixing high-moisture alfalfa with peanut vine in different proportions on the bacterial communities and fermentation characteristics of silage. The high-moisture alfalfa and peanut vine were mixed at ratios of 10:0 (CK), 8:2 (TI), 7:3 (T2), 6:4 (T3) and 5:5 (T4), respectively. For each treatment, silos (25 × 35 cm) were anaerobically fermented in darkness at room temperature and analyzed after 45 days. The results showed that the CK silage was weakly fermented, as indicated by a low lactic acid concentration, a high pH value, and high levels of propionic acid (PA), butyric acid (BA) and ammonia nitrogen (NH3-N). As the proportion of peanut vine in the mixture increased, the pH level decreased, and levels of BA, propionic acid, NH3-N, crude protein(CP), nonprotein nitrogen and soluble protein also declined (p < 0.05), while the lactic acid concentration increased and levels of neutral detergent fiber (NDF) and water-soluble carbohydrates (WSC) also rose (p < 0.05). A protein component analysis of silage mixtures using the Cornell Net Carbohydrate and Protein System (CNCPS) showed that the content of the nonprotein nitrogen component (PA) decreased when the proportion of peanut vine increased, whereas the content of rapidly degraded protein (PB1) increased. Mixing with peanut vine also influenced the distribution of the bacterial community. Compared with the CK silage, the relative abundances of Enterococcus, Garciella and Anaerosporobacter in T2, T3 and T4 were significantly lower, while the relative abundance of Lactobacillus was significantly higher. In the T2, T3 and T4 groups, Garciella and Anaerosporobacter were not detected. In summary, in this study, we ensiled high-moisture alfalfa, which was weakly fermented. We found that mixing with peanut vine improved fermentation quality and optimized the structure of the bacterial community. Therefore, to improve the fermentation quality and nutritional value of silage, high-moisture alfalfa should be ensiled with at least 30% peanut vine.