A framework to assess life cycle nitrogen use efficiency along livestock supply chains

to the significant contribution of the livestock sector to nitrogen (N) losses, improving N use efficiency (NUE-N) along the life cycle of livestock products is one of the important step towards increasing production performance and reduction of its environmental impacts. We developed a comprehensive framework and novel metrics to assess NUE-N along the livestock supply chain (i.e. -to-primary- ). Our framework was illustrated for the case study of mixed dairy production in Western Europe. Metrics developed included the life cycle NUE-N; total N losses to the environment per unit of N in the final co-products; and the N hotspot index (NHI-N), defined as the relative evenness of the N losses along the supply chain. Averaged across countries, the life cycle NUE-N was 36¿3.1%, N losses were 6.6¿1.8 g N per g N in the final animal co-products, and NHI-N of 1.0¿0.1. The N losses and NHI-N also revealed large differences in hotspots across supply chains, and allowed to identify priority areas where improvement actions are necessary to enhance the efficiency. We show that the combination of life cycle NUE-N, N losses and NHI-N gives valuable information to guide N management in livestock supply chain