Linked swine feed balanced strategy and manure management systems: Dual mitigation of nutrient element excretion and composting gaseous emissions

• Low protein balanced diet (LPBD) increased C and N absorption and reduced pollutant excretion. • LPBD pig manure-sawdust (LPSD) composting reduced CO 2 , CH 4 , N 2 O, and NH 3 emissions. • LPBD manure altered compost conditions, influencing microbes and genes to cut GHGs and NH 3 . Intensive swine production causes nutrient losses and enhanced gaseous emissions during manure management, which disrupts nutrient cycling within agricultural systems and threatens agroecosystem sustainability. Prior research has typically examined feeding and manure management as isolated processes, failing to integrate these two components to improve system performance, and this gap limits the design of integrated agricultural systems. Here, we implemented a low-protein balanced diet (LPBD) system and compared it with a high-protein traditional diet (HPTD) to evaluate impacts on swine growth performance and nutrient-use efficiency, followed by sawdust co-composting of the resulting manures. System responses were quantified through integrated monitoring of nutrient excretion, compost physicochemical properties, and gaseous emissions, together with metagenomic profiling of microbial communities and functional genes and subsequent path modeling to resolve key interaction pathways across the feed–compost agricultural system. We found that LPBD improved C/N digestion synchronization, reduced protein/energy excretion, and maintained swine productivity, while markedly decreased CO 2 , CH 4 , N 2 O and NH 3 emissions during composting. Metagenomics indicated that LPBD enriched N-cycling genes ( nirK, nosZ, nifH ) and restructured CAZyme repertoires and microbial communities, patterns consistent with lower NH 3 emissions and enhanced carbon cycling. Path modeling further indicated that diet-driven shifts in compost composition altered environmental factors and indirectly regulated gas emissions via enzymatic and genetic pathways. Overall, this integrated feed–compost strategy links livestock nutrition with environmental management, enhances nutrient cycling efficiency at the agroecosystem level, and provides a basis for sustainable, low-emission circular livestock systems.