Upcycling food leftovers and grass resources through livestock: Impact of livestock system and productivity

Consumption of animal-source food is criticised, among other reasons, for its relatively high environmental impact. It is, however, increasingly acknowledged that livestock can contribute to nutrition security if they upcycle low-opportunity-cost feed (LCF) – food waste, food processing by-products and grass resources – into nutritious animal-source food. So far, however, no study explored the allocation question “to which livestock should we feed what LCF to maximise livestock's contribution to human nutrition”. Here we optimise the use of the LCF available in the EU, using a model that assigns LCF to those livestock systems that maximise animal protein production. We included the five most common livestock systems in the EU – pigs, laying hens, broilers, dairy cattle and beef cattle – considering their nutrient requirements under three productivity levels (low, mid and high). LCF availability is based on current food supply combined with food wastage and food processing data, and current grassland productivity. Our results showed that optimal conversion of LCF available in the EU, could supply 31 g animal protein per EU capita per day. We confirmed that this optimal conversion requires a variety of both livestock systems and productivity levels. Dominant livestock systems were those that have a high conversion efficiency (laying hens, dairy cattle), were best able to valorise specific LCF (dairy cattle for grass; pigs for food waste), and could valorise low quality LCF because of their low productivity. Limiting the model to use only conventional, high productive, livestock reduced animal protein supply by 16% to 26 g/(cap*d). Besides the efficiency with which livestock used the available LCF, the estimated protein supply from livestock fed solely on LCF, was sensitive to assumptions regarding the availability and quality of LCF, especially grass resources. Our model provides valuable insights into how livestock can efficiently use LCF, which is essential for a transition towards a circular food system.