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Nitrogen plays an important role in animal production because it is essential for the production of animal tissue, milk, eggs and wool. Grasses provide more than 70% of the global protein intake by animals. Two-thirds of the remaining protein is supplied by feedstuffs and one-third by products like kitchen wastes. The global efficiency of nitrogen in animal production is slightly over 10%, with the result that 102 Tg (1012 gram) nitrogen are excreted on a yearly basis by all domesticated animals. This article presents the nitrogen balance sheets for global animal production, global crop production and the global agricultural sector. It discusses the present nitrogen efficiency in animal production and possible improvements. For a sustainable world it is necessary to study and to establish the desired balance between human food and animal feed production.