Ensiled Pleurotus ostreatus based spent mushroom substrate from corn: In vitro gas production, greenhouse gas emissions, nutrient degradation, and ruminal fermentation characteristics.

The present study evaluated varying inclusion levels (10%, 20%, 30%, 40%, and 50%) of spent mushroom substrate (SMS) derived from Pleurotus ostreatus, ensiled for 0, 21, 42, and 64 d, using an in vitro batch culture technique. The study employed a 6 × 4 factorial design with six inclusion levels and four ensiling durations. The batch culture was conducted over 24 h across two runs. Gas production (GP), greenhouse gases (GHG) production, nutrient degradability, and volatile fatty acids (VFA) were measured. Significant interactions (P < 0.01) between ensiling duration and diet were observed for the concentrations of different nutrients and GHG production. SMS levels in diets increased (P < 0.001) dry matter (DM), neutral (NDF), and acid (ADF) detergent fiber concentrations but decreased crude protein (CP) and cellulose levels. Ensiling period decreased (P < 0.001) DM, NDF, acid-detergent lignin (ADL), and hemicellulose concentrations but increased non-structural carbohydrates (P < 0.05). Diets with higher SMS levels had lower (P < 0.001) GP, methane (CH₄), and carbon dioxide (CO₂) production, together with increased degradability of DM, NDF, ADF, and ADL. Conversely, extending ensiling increased CH₄ and CO₂ production, degradability of DM, and proportions of acetate and propionate but decreased NDF and ADF degradability. Total VFA and butyrate were highest (P < 0.05) in the diet with 50% SMS inclusion. In conclusion, SMS can replace up to 50% of corn silage in the diets of beef and non-lactating dairy cows; however, extending the ensiling duration is not recommended.