Synergistic Effects of Wheat Bran and Inoculants on Fermentation and Nutritional Quality of Soybean Straw Silage

The efficient valorisation of lignocellulosic biomass from soybean straw into high-quality silage remains a pressing challenge for sustainable livestock production. This study employed a 3×3 factorial design to systematically investigate the interactive effects between wheat bran additions (0%, 10%, 20% of fresh weight) and microbial inoculant regimes (control, Effective Microorganisms, EM+Trichoderma longibrachiatum) on soybean straw silage quality. Two-way ANOVA revealed significant main effects and interactions between these factors across multiple quality parameters, providing novel insights into their mechanistic relationships. The strategic combination of these additives significantly enhanced silage quality, with crude protein content increasing by up to 12% (reaching 18.52% in optimal treatments), fiber fractions decreasing significantly (NDF reduced by 8.7%), and pH declining from 5.44 to 4.43, thereby elevating relative feed value by 16 points (P<0.05). Most notably, all 10% wheat bran treatments completely suppressed butyric acid production. The 10% wheat bran plus EM inoculant (W2T2) treatment emerged as particularly effective, achieving optimal lactic:acetic acid ratio (4.5:1) while maintaining negligible butyric acid production. Unexpectedly, 20% wheat bran without inoculant (W3T1) yielded the highest relative feed value (142.73), suggesting that higher wheat bran levels provide both sufficient fermentable carbohydrates and an indigenous microbial community capable of effective fermentation. This research advances our understanding of enzymatic bioconversion of recalcitrant lignocellulosic structures through specific substrate-inoculant threshold combinations that optimize silage quality via synergistic interactions rather than additive effects alone. These findings offer a scientifically grounded approach to transform abundant low-quality crop residues into high-value animal feed, simultaneously addressing feed security challenges, mitigating agricultural waste, and promoting circular agricultural systems.