Abstract

The marine endophytic fungus Aspergillus terreus has considerable potential to improve the utilization of lignocellulosic feed through its fibrolytic and ligninolytic activities. Therefore, the effects of A. terreus supplementation on rumen microbial populations, fermentation characteristics, methane production, and fiber digestibility were evaluated using an in vitro rumen incubation system. A completely randomized design with four treatments and five replications was used. The treatments consisted of a control diet (30:30:40 mixture of Napier grass, palm leaves, and concentrate) and the control diet supplemented with A. terreus at 1.5% (0.75 mL of fungal suspension at 106 CFU/mL−1), 3.0% (1.5 mL of fungal suspension at 106 CFU/mL−1), or 4.5% (2.25 mL of fungal suspension at 106 CFU/mL−1). The measured variables included ruminal pH, ammonia (NH3) concentration, volatile fatty acid (VFA) production and profiles, microbial populations, estimated methane production, dry matter digestibility (DMD), organic matter digestibility (OMD), and fiber fraction digestibility. Supplementation with A. terreus at 1.5%–3.0% significantly (p < 0.05) increased the digestibility of neutral detergent fiber, hemicellulose, cellulose, and lignin. Lignin digestibility increased from 28.22% in the control to >60% in the fungal-supplemented treatments, indicating strong ligninolytic activity. However, acid detergent fiber digestibility and microbial populations were unaffected. Most rumen fermentation parameters, including NH3 concentration, total VFA production, VFA molar proportions, the acetate-to-propionate ratio, and estimated methane production, remained unchanged. Ruminal pH decreased slightly at the 3.0% inclusion level, whereas DMD and OMD decreased at the 4.5% supplementation level (p < 0.05). Overall, A. terreus supplementation improved structural carbohydrate degradation, particularly the digestibility of lignin, hemicellulose, and cellulose, without adversely affecting rumen fermentation. An inclusion level of 1.5%–3.0% appears to be optimal for enhancing fiber utilization under in vitro conditions.