The Effects of Adding Walnut Green Husk on the Quality of Alfalfa Mixed Silage, Protein Degradation, Microbial Community, and Their Interrelationships

<b>Objectives</b>: This experiment was conducted to investigate the effects of adding walnut (<i>Juglans regia</i> L.) green husk (WGH) on the quality of alfalfa mixed silage, protein degradation, microbial community, and their interrelationships. <b>Methods</b>: Alfalfa (<i>Medicago sativa</i> L.) fresh grass and WGH dried powder were used as raw materials to prepare three mixed silages of alfalfa fresh grass with 80 g/kg (A1), 120 g/kg (A2), and 160 g/kg (A3) of WGH dried powder, respectively, with alfalfa fresh grass silage as the control group (CK). After 60 days of ensilage, samples were taken and analyzed, with three replicates per treatment. <b>Results</b>: WGH treatment significantly improved alfalfa silage fermentation and nutritional quality. It reduced undesirable fermentation products while promoting beneficial lactic acid bacteria and preventing mold growth. Increasing the WGH ratio enhanced dry matter content and digestibility, with only a minor effect on crude protein. These results suggest that WGH is an effective silage additive for improving both fermentation characteristics and feed value. With the increase in the proportion of WGH, the proportions of rapidly degradable protein (PB1) and medium rate degradable protein (PB2) increased linearly, while the proportions of free amino acid nitrogen (FAA-N), peptide nitrogen (Peptide-N), slow degradable protein (PB3) and binding protein (PC) decreased linearly and the protease activity decreased significantly (<i>p</i> < 0.05). Bacterial community analysis showed that the relative abundance of <i>Lactiplantibacillus</i> and <i>Levilactobacillus</i> in the silage increased after WGH was added, while the relative abundance of <i>Acetobacter</i>, <i>Pantoea</i>, <i>Weissella</i> and <i>Serratia</i> decreased. <b>Conclusions</b>: Compared with pure alfalfa silage, the addition of WGH has a positive effect on silage quality, protein degradation and bacterial community structure, and the addition of WGH with 120 g/kg is more suitable.