Effects of Protein Supplementation and Microbial Inoculation on Fermentation Quality, Aerobic Stability, and In Vitro Digestibility of Maize Silage

Maize silage is widely used due to its high fermentability but requires protein supplementation, commonly from soybean meal (SBM). Rising costs have driven interest in alternative protein sources, while microbial inoculants are used to improve silage fermentation and stability. This study evalu-ated the effects of partially replacing SBM with marula oilcake (MOC), with or without bacterial inoculants, on maize silage fermentation characteristics, nutrient preservation, aerobic stability, and in vitro digestibility. Whole-crop maize (< 38% dry matter) was supplemented with SBM or MOC, treated with either Lalsil Fresh or Sil-All 4x4®, and ensiled anaerobically for 90 days. Post-ensiling analyses included chemical composition, fermentation end-products, microbial populations, aerobic stability, volatile fatty acid profiles, gas production, and in vitro digestibility. Fermentation quality, nutrient composition, and aerobic stability differed significantly among treatments (P < 0.05). SBM-based silages exhibited greater lactic acid production, higher crude protein and digestibility, but also elevated butyric and branched-chain volatile fatty acids, indicating increased proteolysis. In contrast, MOC-based silages showed lower lactic acid concentrations and digestibility but reduced butyric fermentation, suggesting improved protein preservation. Microbial inoculants enhanced fermentation parameters more effectively in SBM than in MOC silages. These results indicate that protein source and inoculation strategy markedly influence maize silage fermentation outcomes, highlighting the need for further processing of alternative protein supplements to optimize silage quality.