Impact of Solid-State Fermentation on Nutrient Profile, in vitro Gas Production Dynamics, and Methane/Carbon Dioxide Emissions of Selected Tropical Forages

Abstract

Aims: This study investigated the effects of solid-state fermentation (SSF) on the nutritional composition, phytochemical profile, in vitro gas production, fermentation kinetics, and CH₄/CO₂ emissions of three tropical forages, addressing the need to improve forage quality and reduce enteric methane emissions in tropical ruminant production systems. Place and Duration of Study: Forages were sourced from the paddocks of the Department of Animal Science, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. Brachiaria mulato II, Megathyrsus maximus, and Cenchrus purpureus, harvested after 120 days of regrowth, were fermented for 30 days with Aspergillus niger, Aspergillus oryzae, and Trichoderma spp. under aerobic conditions. Study Design: A 3 × 3 factorial arrangement in a completely randomised design was used, with treatments replicated three times and analysed for proximate, fibre, phytochemical, and in vitro gas production parameters. Results: SSF significantly (P = .05) enriched crude protein, with TS_CP recording the highest value (12.26%). Neutral detergent fibre was reduced most in AN_CP (53.20%). Anti-nutritional factors, including tannins (80.70–97.47 mg/100 g), saponins (35.44–56.12 mg/100 g), oxalates (8.96–17.30 mg/100 g), and alkaloids (8.45–14.18 mg/100 g), were reduced, whereas flavonoids and phenols increased. TS_CP produced the highest gas volume (11.75 mL/200 mg DM) and the fastest fermentation rate (c = 0.045 h⁻¹), yet it also generated the greatest CH₄ (3.50 mL/200 mg DM) and CO₂ (5.00 mL/200 mg DM) emissions. Conclusion: Fungal SSF substantially improved tropical forage nutritional quality and digestibility; however, the trade-off between superior fermentation performance and elevated greenhouse gas emissions underscores the importance of deliberate forage-fungus combination selection for sustainable livestock production.