Life cycle assessment of Japanese pig farming using low-protein diet supplemented with amino acids

Livestock production is indicated to be one of the major emitters of greenhouse gases (GHG), particularly methane (CH4) and nitrous oxide (N2O), around the globe, and the reduction of these emissions is an important goal. GHG emissions as well as other environmental impacts of two pig (Sus scrofa domesticus) farming systems, one using conventional diets (CNV) and the other using low-protein diets supplemented with crystalline amino acids (LOW), were therefore evaluated by comparative life cycle assessment (LCA) focusing on manure management and by cradle-to-farm gate LCA. The functional unit was defined as one marketed pig. For the comparative LCA of manure management, the CH4 and N2O emissions from manure management of CNV were set as a baseline, and the system boundary of LOW included the CH4 and N2O emissions from manure management, and changes in the GHG emissions from feed production including amino acid manufacturing, feed transport, and the materials and energy consumed in manure management. For the cradle-to-farm gate LCA of pig farming, the evaluated system included the processes of feed production including amino acid manufacturing for LOW, feed transport, animal housing including the biological activity of the animal, and manure management. The results of the comparative LCA showed that the GHG emissions from manure management of LOW were 20% less than those of CNV, and the GHG reduction rate of LOW compared to CNV was even greater in the case of a stricter target of effluent nitrogen content. The results of cradle-to-farm gate LCA showed that LOW had lower GHG emissions, acidification potential, eutrophication potential and overall environmental impact, and slightly larger energy consumption, than CNV. The sensitivity analysis showed that LOW still had less GHG emissions than CNV, even in the least preferable case assuming a 40% lower reduction rate of nitrogen excretion.