This study utilized rapeseed straw as the raw material and employed a completely randomized design with four treatments: a distilled water control (CK), individual supplementation of Lactiplantibacillus plantarum (1.0 × 10⁶ CFU/g fresh weight) (Lp), individual supplementation of xylanase (50,000 U/g fresh weight) (XY), and a combined bacterium–enzyme treatment (XYLp). Each treatment was replicated five times, vacuum-sealed, and fermented at 25 °C for 60 days to systematically evaluate the effects of different treatments on the fermentation quality, nutritional composition, and microbial community structure of rapeseed straw silage. The results demonstrated that, compared with the CK group, all additive treatments significantly decreased pH and increased lactic acid (LA) content (p < 0.05). Among them, the Lp group exhibited the lowest pH value (4.27), which was significantly lower than all other treatments except XYLp (p < 0.05). Both the Lp and XYLp groups showed significantly higher LA content than the other groups (p < 0.05). Crude protein (CP) content was significantly higher in all additive treatments than in the CK group (p < 0.05). The XYLp group exhibited the most substantial fiber degradation, with acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents being significantly lower than CK and reaching the lowest values among all treatments (p < 0.05). Both the XY and XYLp groups showed significantly lower hemicellulose and holocellulose contents compared to the CK and Lp groups (p < 0.05). Microbial community analysis revealed that the synergistic bacterium–enzyme treatment significantly enriched fibrolytic genera, including Kosakonia and Pediococcus, and upregulated the expression of key fibrolytic enzymes such as cellulase (EC: 3.2.1.4), β-glucosidase (EC: 3.2.1.21), and endo-1,4-β-xylanase (EC: 3.2.1.8). Functional prediction further indicated that the bacterial–enzyme synergy enhanced fibrous structure degradation and fermentable substrate release by activating carbohydrate metabolism pathways and bacterial secretion systems. These findings suggest that the combined application of Lactiplantibacillus plantarum and xylanase has the potential to be a promising strategy for enhancing fiber degradation and overall fermentation quality in rapeseed straw silage.

This study aimed to screen high-yield and high-quality sorghum–sudangrass hybrid varieties suitable for popularization and cultivation in the Hulunbuir region through a comprehensive evaluation of silage fermentation quality and bacterial community. Comparative analyses were conducted on six sorghum–sudangrass varieties, namely, sorghum–sudangrass hybrid 3 (SS1), sorghum–sudangrass hybrid 4 (SS2), sorghum–sudangrass hybrid 5 (SS3), sorghum–sudangrass hybrid 7 (SS4), sorghum–sudangrass hybrid 8 (SS5), and Super Sugar–Dwarf Sorghum (SS6). The harvested sorghum–sudangrass at the late milk stage was chopped, vacuum-sealed in polyethylene bags (30 cm × 40 cm), and subjected to 60 days of ensiling fermentation. The results revealed significant differences among different varieties (p < 0.05). SS2 achieved the highest fresh herbage yield of 78.26 t/hm², while the fresh yield of SS4 was 57.39 t/hm², approximately 26.7% lower than that of SS2. However, SS4 exhibited superior quality, with the thickest stem diameter of 20.26 mm (p < 0.05). It exhibited the highest crude protein content, reaching 5.72% DM; its silage pH was relatively low, at only 3.71 (p < 0.05); its fiber content was significantly reduced (acid detergent fiber, ADF = 40.03% DM, p < 0.05); and it was rich in Lactococcus and Lactobacillus (p < 0.05). The ensiling process of SS4 highly significantly decreased bacterial diversity (p < 0.01) and shifted the dominant bacterial phylum from Proteobacteria to Firmicutes. Functional prediction indicated that the bacterial community of SS2 possessed the highest predicted abundance of functional genes related to cellulase and beta-glucosidase (p < 0.05). Our findings suggest that SS2 should be prioritized for production systems aiming for maximum biomass accumulation, whereas SS4 is recommended as a superior variety for high-quality animal nutrition systems where fermentation stability and nutrient preservation are paramount.