Net protein contribution and enteric methane production of pasture and grain-finished beef cattle supply chains.

Ruminant red meat production systems around the world often include a grain feeding phase. The role of red meat in the food system is therefore often discussed in terms of the food vs feed debate, as well as invoking the comparatively poor feed conversion efficiency of ruminants and climate impacts from enteric methane. The concept of net protein contribution (NPC) incorporates the quality attributes of protein produced by livestock systems into estimates of the efficiency of production systems. We applied the NPC method to two Australian beef supply chains, i) Grass-fed and ii) Grain-finished beef, using an established model of ruminant grazing systems (GrassGro®) and these are reflective of beef production systems in other countries. The beef supply chains evaluated did not compete with humans for protein. The Grain-finished beef supply chain, while positively contributing to human protein requirements (NPC value 1.96), had markedly lower NPC values than the Grass-fed system (NPC value 1 597). However, Grass-fed beef production systems have a higher methane intensity than the Grain-finished supply chain. The two examples of pasture-based beef production systems examined provide a positive net protein contribution to human food supply, even with extended periods of finishing on grain-based diets. This is achieved by ruminant grazing on pastures converting low-quality forage into high value human edible protein. The efficiency of protein production varies according to the system design, and other considerations such as land use and enteric methane production are elements that need consideration in the overall assessment of the production footprint.