From manure to insects: circular transformation of livestock manure for nitrogen and greenhouse gas mitigation

Livestock manure, enriched with essential nutrients, represents a promising feedstock for insect farming. Insect protein offers a circular and high-quality alternative to conventional crop-based livestock feed, potentially reducing both environmental and resource pressures. In this study, we integrate global livestock models with trade, land-use, and cost-benefits analysis to quantify the environmental and economic implications of manure-to-insect conversion while ensuring the recycling of manure to croplands to maintain soil fertility across 166 countries. Our analysis show that scaling up this pathway could yield approximately 4.2 million tons (Mt) of insect protein N to substitute crop-based feed, and releasing up to 45 million hectares of cropland. This transition could mitigate N and GHG emissions by 6.0 Mt N and 1,266 Mt CO₂-e during feed cultivation and manure storage. The residual manure, after insect processing can be returned to fields as a high-quality and stable organic fertilizer, offsetting 23 Mt N of synthetic fertilizer demand. With an estimated implementation cost of 25 billion USD, this strategy could deliver combined economic and environmental benefits of 225 billion USD. These results highlight manure-based insect farming as a scalable, cost-effective, and circular solution for reducing global agricultural pollution and enhancing food system resilience. This pathway demonstrates how reimagined nutrient cycles can mitigate planetary health challenges by integrating food security, climate mitigation, and sustainable resource use within a unified circular framework.