The increasing and changing demand for livestock products has led to the transformation of production systems across the world: from local, small-scale, mixed crop-livestock systems to global, demand-driven supply chains. How feed is produced and consumed has also changed, with more large-scale livestock farms relying on internationally traded feed materials. These changes have altered the nitrogen (N) biogeochemical cycles, leading to N emissions into the environment around the planet at various temporal and spatial scales.

According to the article, Nitrogen emissions along global livestock supply chains, published in Nature Food, the livestock sector is a major user of natural resources through feed whose production requires annually 76 Tg N y^-1 of synthetic fertilizer and biological N fixation, globally. 

The authors found that livestock emissions represent one-third of human-induced N emissions, globally. These N emissions are associated with the widespread use of synthetic fertilizer and applied manure in cropland and grassland, manure management systems, and the transport of N-rich products such as feed, food and manure. N emissions cause environmental impacts such as climate change, acidification, eutrophication and biodiversity losses, and can also be harmful to human health. 

The article highlights the importance and diversity of livestock systems and the resulting N emissions, including international trade. The study, covering 275 countries and territories grouped in 10 different regions, quantifies N-use indicators of life-cycle nitrogen use efficiency and life-cycle net nitrogen balance, identifies hotspots of N emissions, and suggests targeted interventions to reduce emissions.

The study highlights how ruminant systems (cattle, buffalo, goats, and sheep) globally account for 71 percent of total N emissions from livestock, with pork production and the production of eggs and meat from chickens contributing the remaining 29 percent. Most N emissions occur in South Asia and East and Southeast Asia (63%). The study argues that these N emissions will continue to increase, given the projected expansion of animal production in the coming decade. 

At the same time, the N indicators across regions and systems underscore the variability across countries and livestock systems, with significant differences between livestock management practices, feed resources, animal performance, size of production units and agro-ecological zones. The embedded N emissions associated with internationally traded feed and animal-sourced food represent about 8 percent of total N emissions.

The analysis will help to identify opportunities to improve sustainable nitrogen management while increasing livestock systems’ efficiency and reducing environmental impacts, as recognized in the United Nations Environment Assessment resolution (UNEP/EA.4/L.16) on sustainable nitrogen management.

This research was based on the updated FAO Global Livestock Environmental Assessment Model (GLEAM). According to the authors of the paper, the research is partially aligned with the guidelines for the assessment of nutrient flows and associated environmental impacts in livestock supply chains developed by FAO’s Livestock Environmental Assessment and Performance (LEAP) Partnership.