Mixed ensiling of drought-impaired grass with agro-industrial by-products and silage additives improves the nutritive value and shapes the microbial community of silages

Droughts lead to reduced biomass production and unfavourable nutrient composition in grassland. As an alleviation, yet unexploited strategy, mixed ensiling of grass with agro-industrial by-products may improve the ensilability and nutritive value of drought-impaired grassland. This study investigated first whether mixed ensiling of drought-impaired grass with either sugar beet pulp (SBP), wheat gluten feed (WGF) or brewers' grains (BG) has a beneficial impact on chemical composition, fermentation characteristics, in vitro gas production (GP) and physically effective neutral detergent fibre (peNDF) of silages. Secondly, it was tested whether the application of anaerobic fungi culture supernatant (AF), mixed ruminal fluid (RF) or lactic acid bacteria (LAB) provides further advantages. Additionally, the microbial community composition was evaluated in selected silages. All silages showed satisfying conservation characteristics with high lactic acid levels and low dry matter losses, and peNDF values typically found for conserved forages. Mixed ensiling with BG substantially increased the crude protein concentration, whereas SBP increased the total degradability and WGF enhanced both. The further addition of fresh AF resulted in the overall highest lactic acid levels, especially in SBP-based silages, but without changes in in vitro GP. The in vitro GP was higher with RF, particularly in mixed silages, suggesting an improved degradability. The LAB-treated silages showed lower pH compared to controls, but had no impact on in vitro GP kinetics. Concluding, mixed ensiling holds potential to produce high-quality silages from drought-impaired grassland. The further addition of silage additives can be useful for certain substrates, but appeared not mandatory.