Fermentation quality and microbial communities of mixed silage from Pennisetum glaucum × purpureum and Rosa roxburghii residue

This study investigates the mechanism by which varying mixing ratios of Pennisetum glaucum × purpureum and Rosa roxburghii residue influence the overall quality of silage feed. A completely randomized design with three replicates per treatment was used. By establishing mixed fermentation ratios of Pennisetum glaucum × purpureum and Rosa roxburghii residue at 0:100 (R), 20:80 (P20), 40:60 (P40), 60:40 (R40), 80:20 (R20), and 100:0 (P), the study systematically measured the nutritional components, fermentation quality, Cornell Net Carbohydrate and Protein System (CNCPS) protein fractions, and microbial community structure of the mixed fermented products. Analysis was conducted using Kyoto Encyclopedia of Genes and Genomes (KEGG) functional prediction and correlation networks. The results indicate that at mixing ratios of 60:40 (R40) or 80:20 (R20), silage quality was optimal: the content of starch in the feed significantly increased, fiber content decreased, lactic acid levels markedly rose to 1.35–1.67 g/kg DM, and pH dropped to 3.60–3.63, while both ammonium nitrogen (AN) and butyric acid levels remained low. The analysis of CNCPS protein fractions revealed a high retention of true protein, accompanied by a notable decrease in the proportion of nonprotein nitrogen (NPN). Microbial community analysis showed that these optimal mixing ratios were associated with higher relative abundances of beneficial lactic acid bacteria (Levilactobacillus and Lactiplantibacillus) and lower abundances of potentially harmful bacteria (Enterobacter). Functional predictions further indicated that these microbial shifts correlated with enhanced metabolic pathways, including carbohydrate metabolism. In summary, mixing Pennisetum glaucum × purpureum and Rosa roxburghii residues at 60:40 or 80:20 ratios are associated with improved substrate composition and microbial ecology. This approach not only enhances the nutritional value and fermentation stability but also improves the preservation efficiency of silage protein, thereby providing a viable technical solution and theoretical foundation for the utilization of agricultural byproducts and the production of high-quality silage.