Nutritional Strategies for Methane, Nitrogen, and Phosphorus Mitigation in Ruminants: Mechanisms, Applications, and Regional Adaptations

Against the background of the ongoing transition toward green livestock production and the implementation of “dual-carbon” goals, reducing the environmental footprint of ruminant production while maintaining animal performance has become a key focus in nutritional regulation research. This review summarizes and critically discusses the mechanisms and recent progress of nutritional strategies for emission mitigation and improved nutrient utilization in ruminants, with particular emphasis on major environmental challenges, including enteric methane emissions and nitrogen and phosphorus losses. The review discusses the underlying mechanisms through which nutritional interventions contribute to emission reduction, focusing on ruminal hydrogen flux allocation, microbial community remodeling, host metabolic responses, and changes in nutrient utilization efficiency. In addition, by integrating functional feed additives, diet formulation optimization, precision protein supply, and mineral nutrition regulation, this review compares the application characteristics and practical challenges of different strategies in mitigating methane emissions, reducing nutrient excretion, and sustaining production performance. Furthermore, research approaches such as in vitro screening, multi-omics analysis, and evidence synthesis approaches are discussed to highlight the shift of green nutritional technologies from single-target interventions toward integrated and system-level regulation. This review provides a theoretical basis and technical reference for developing green ruminant production systems that balance productivity, animal health, and environmental sustainability.