Usage of by-products and residues of the food system in livestock diets leads to savings in global land and water resources

Animal foods play an important role in human nutrition providing essential micro and macronutrients. In addition, animal-source foods cover 16% of the global food supply, so contribute to global food security. However, livestock consumes about 70% of the global agricultural land and one-third of the freshwater available for agriculture, thus fueling the debate on the competition between the food and the feed sector for the use of increasingly scarce natural resources. Several studies suggest that more efficient management in the food system can reduce competition and increase the global food supply without further pressure on resources. Here we propose a strategy consisting in the replacement of energy-rich food-competing feeds, such as cereals and tubers, with agricultural by-products and residues. Thus, we analyze both the current impact on land and water use for animal-source foods and the natural resources (i.e. land and water) saving associated with the replacement. To this aim, we collected data on regional feed use and the potential replacement of these feeds with actually available by-products and residues. Then, the collected data are combined with countries-specific crop yields and a dynamic spatially distributed and physically based agro-hydrological model to analyze the difference in the land and water use between the current baseline condition and the substitution scenario. Considering the replacement of five major cereals and cassava estimated to range between 11% to 16% of their feed use, the potential amount of fertile land and green water volume that could be saved ranges from 10% to 14%, while from 11% to 17% for the blue water volume. While Eastern Asia and North America would reduce their energy-rich feed crop consumption the most, would be Southern, Eastern, and South-Eastern Asia, and Eastern Europe that would benefit the most from the use of agricultural by-products and residues to save land and green water resources. As far as blue water is concerned, the highest savings are expected to occur in Asia, where cereal production is traditionally irrigated, although linked to unsustainable water withdrawals. Furthermore, the effect of trade on the consumption of natural resources, namely virtual land and water trade, is also explored, with feed crop production relocated through virtual resource flows. While Eastern Europe, Northern America, and South America appear as net land and green water exporters, Eastern and Western Asia and Southern Europe appear as net importers, and Western Europe, instead, as both an importer and exporter region through feed trade. On the other hand, Asia and Northern America appear to be net freshwater exporters. As the demand for livestock products grows over the next half-century, any strategy aimed at curbing the demand for primary commodities and making the food system more resilient has the benefit of reducing environmental impacts on both local and distant areas of the world but also the trade dependency of countries, in a time where global food security is threatened by several factors.