In Vitro Evaluation of the Potential of Cashew Nut Shell Waste for Circular Nutrient Flows and Methane Mitigation in Ruminant Systems

Abstract

Indonesia’s agro-industrial sector generates large amounts of by-products, with cashew nut shells representing a major waste stream from cashew processing. Within the framework of agroecology and regenerative practices, valorizing this residue is essential to support circular nutrient flows, reduce environmental pressure, and enhance the sustainability of livestock systems. This study aimed to evaluate the potential of cashew nut shell waste as a ruminant feed ingredient, with emphasis on nutrient recycling, rumen fermentation efficiency, and enteric methane mitigation. An in vitro experiment was conducted using diets pelleted with graded inclusion levels of cashew nut shells at 0%, 2.5%, 5%, and 7.5% of dietary dry matter. Measurements included nutrient digestibility, rumen fermentation characteristics, and methane production. The results showed that increasing cashew nut shell inclusion significantly reduced methane emissions, reaching a 34% reduction at the highest inclusion level. Digestibility declined with increasing inclusion levels but remained within acceptable ranges, indicating a balance between nutrient utilization and environmental benefits. Higher inclusion levels reduced ruminal pH and ammonia concentrations while increasing total volatile fatty acid production. These responses indicated improved fermentation efficiency and more efficient nitrogen utilization. The findings demonstrate the role of agro-industrial by-products in supporting regenerative livestock systems through waste valorization and emission mitigation. Cashew nut shell waste shows strong potential as a sustainable feed resource that enhances circular nutrient flows and contributes to climate-smart, agroecological ruminant production systems