Co-ensiling corn silage with Pleurotus-based spent mushroom substrate and oilseeds: Impacts on rumen fermentation, digestibility, and methane emissions in a RUSITEC system

The present study examined the effects of partially replacing corn silage (CS) with Pleurotus-based spent mushroom substrate (SMS) and oilseeds (OS) on rumen fermentation characteristics, nutrient digestibility, volatile fatty acid (VFA) profiles, and greenhouse gas emissions using a rumen simulation technique (RUSITEC). Four silages were evaluated: A control diet containing 100% CS and three co-ensiled treatments in which CS was partially replaced with Pleurotus-based SMS and OS. The oilseed fraction consisted of equal proportions of soybean and canola seeds. The treatments were: CS90 (90% CS + 5% SMS + 2.5% soybean seed + 2.5% canola seed), CS80 (80% CS + 10% SMS + 5% soybean seed + 5% canola seed), and CS60 (60% CS + 20% SMS + 10% soybean seed + 10% canola seed). Dry matter (DM), organic matter, and crude protein contents were not affected by treatment, whereas ash content increased (P < 0.001) with increasing SMS-OS inclusion. Increasing SMS-OS inclusion significantly reduced non-fiber carbohydrates, hemicellulose and cellulose, while ether extract, neutral detergent fiber, acid detergent fiber, and acid detergent lignin concentrations were increased (P < 0.05). Ruminal fermentation pH, effluent volume, and total gas production showed only numerical differences or trends. DM digestibility increased markedly with SMS-OS inclusion (P < 0.001), rising from 38.7% in the control to 53.0, 49.9, and 52.5% in CS90, CS80, and CS60, respectively, representing improvements of approximately 29–37%. In CS90, organic matter digestibility remained high (P < 0.001) and fiber digestibility was largely the same. Moreover, CS90 had the highest total VFA and acetate, whereas CS60 had the highest propionate proportion (P < 0.05). All SMS-OS diets substantially reduced methane production (P = 0.003) and carbon dioxide emissions (P = 0.014) relative to the control. Methane output declined by approximately 60, 45, and 35% in CS90, CS80, and CS60, respectively (34.2–55.6 vs. 85.7 mg/g DM), while carbon dioxide emissions were reduced by about 49, 26, and 17% (134.7–218.4 vs. 264.0 mg/g DM). In conclusion, co-ensiling corn silage with SMS and oilseeds improved DM utilization while influencing methane production, with reductions observed in all the treatments compared with the control without adversely affecting rumen fermentation stability or fiber digestion under RUSITEC conditions.