Inoculum-Level Optimization of Trichoderma viride Pretreatment of Coffee Pulp Improves In Vitro Rumen Fermentation Efficiency and VFA Production

Ruminants contribute substantially to greenhouse gas emissions, particularly methane (CH₄) produced during enteric fermentation. Improving rumen fermentation efficiency through the utilization of agro-industrial by-products is therefore an important strategy for sustainable livestock production. Coffee pulp (CP), an abundant by-product of coffee processing in Indonesia, has potential as an alternative feed resource for ruminants; however, its utilization is constrained by low digestibility. This study evaluated the effects of biological pretreatment of CP using different inoculum levels of Trichoderma viride on volatile fatty acid (VFA) production, gas production kinetics, and methane emission during in vitro rumen fermentation. A completely randomized design was applied with four treatments: TV0 (fermented CP without T. viride), TV5 (fermented CP with 10⁵ spores g⁻¹ T. viride), TV6 (fermented CP with 106 spores g⁻¹ T. viride), and TV7 (fermented CP with 107 spores g⁻¹ T. viride), each with four replicates. Biological pretreatment significantly increased total VFA production (P<0.05), with the highest value observed in TV6 (121.15 mmol L⁻¹), compared with the control (74.40 mmol L⁻¹). Gas production characteristics were also affected by treatment, where TV5 produced the highest cumulative gas production at 72 h incubation (69.50 mL g⁻¹ DM). Methane production and CH₄ percentage were not significantly different (P>0.05). Overall, fermented CP with T. viride improved in vitro rumen fermentation characteristics and increased the utilization potential of CP as an alternative feed resource, with the 10⁶ spores g⁻¹ inoculum level showing the most favorable balance of fermentation responses although its effect on methane mitigation remains inconclusive.