Sustainability evaluation of the large-scale pig farming system in North China: an emergy analysis based on life cycle assessment

At present, the final purpose of livestock production is not only to increase yields but also to improve sustainability. In this study, the characterized results of a life cycle assessment are integrated into an emergy evaluation in terms of potential environmental services to reflect the impact on the sustainability of livestock production systems due to harmful outputs. Concurrently, the life cycle thinking is introduced into the study to diagnose the key points that will improve the sustainability of the system. The assessment was performed through a case study on a large-scale pig farming system in North China. The results of traditional indices indicate that the unit emergy value, emergy yield ratio, emergy loading ratio and emergy sustainability index of the large-scale pig farming system are 5.44E+05 sej/J, 1.00, 3.23 and 0.31, respectively, and reflect the low sustainability of the system. The revised unit emergy value and environmental loading ratio are increased by 76.7% and by 100.3%, respectively, and the revised emergy sustainability index is reduced by 51.6% when the harmful outputs of the large-scale pig farming system are considered. It is clear that the harmful outputs affect the sustainability of the pig production system significantly. Newly designed indices, the resource use efficiency and the unit environmental impact are 8.32E+05 sej/J and 4.17E+05 sej/J, respectively, supporting the efficiency and sustainability from the inputted resource types and outputted perspectives. Furthermore, the case study also shows that from the perspective of the pig life cycle, the improvement of feed composition and labor productivity in the grow-finisher step and the rearing level of breeding pigs are the most important points for the optimization of the large-scale pig farming system. This study is a general supplement to the gap in the assessment of large-scale pig farming in China, and the evaluation results that propose the integration of emergy analysis and life cycle assessment enables a broader view of the sustainability of the production process.