Comparative Evaluation of Crushed Almonds, Peanut Skins, and Water Hyacinth as Alternative Feed Resources for Ruminants: Fermentation Responses and Methane Mitigation Potential

Agro-residues and aquatic biomass are potential sustainable ruminant feeds. However, their effects on rumen digestibility, fermentation, and greenhouse gas emissions remain insufficiently characterized. This study used two in vitro batch culture experiments to evaluate crushed almonds, peanut skins, and water hyacinth as feed additives (1-10%) and grass hay replacements (25-100%). Their chemical composition varied significantly. Crushed almonds are rich in crude protein (22.47%) and ether extract (38.38%). Peanut skins contained moderate protein (13.87%) and high fiber and lignin, while water hyacinth had the lowest protein (7.27%) and highest fiber and ash fractions. All ingredients had no effect on fermentation or methane production when used as additives, whereas grass hay replacement induced marked ingredient-specific responses. Crushed almonds showed the highest in vitro dry matter digestibility (IVDMD), increased propionate, and lowered the A:P ratio; however, methane production increased by 12%. Peanut skins sharply reduced IVDMD with increasing inclusion, resulting in the strongest methane mitigation (57% reduction). Water hyacinth displayed a modestly low IVDMD and moderate methane reduction (14%). In conclusion, methane production is closely associated with substrate degradability, and each ingredient exhibits distinct functional tendencies: crushed almonds enhanced energy availability and digestibility, peanut skins showed methane mitigation potential, and water hyacinth functioned primarily as a low-fermentability grass hay substitute.