Thomas D T, Beletse Y G, Dominik S, Lehnert S A
CSIRO Agriculture & Food, Perth, Western Australia 6014, Australia.
CSIRO Agriculture & Food, Canberra, Australian Capital Territory 2601, Australia.
Animal. 2021 Dec;15(12):100392. doi: 10.1016/j.animal.2021.100392. Epub 2021 Nov 26.
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.
世界各地的反刍动物红肉生产系统通常包括一个谷物喂养阶段。因此，红肉在食品系统中的作用经常在食物与饲料的争论中被讨论，同时也涉及反刍动物相对较差的饲料转化效率以及肠道甲烷对气候的影响。净蛋白质贡献（NPC）的概念将畜牧系统生产的蛋白质的质量属性纳入生产系统效率的估计中。我们使用一个既定的反刍动物放牧系统模型（GrassGro®），将NPC方法应用于澳大利亚的两个牛肉供应链，即：i）草饲牛肉供应链和ii）谷饲牛肉供应链，这两个供应链反映了其他国家的牛肉生产系统。所评估的牛肉供应链并不与人类争夺蛋白质。谷饲牛肉供应链虽然对人类蛋白质需求有积极贡献（NPC值为1.96），但其NPC值明显低于草饲系统（NPC值为1597）。然而，草饲牛肉生产系统的甲烷排放强度高于谷饲供应链。所研究的两个基于牧场的牛肉生产系统的例子，即使在较长时间采用谷物饲料育肥的情况下，也对人类食物供应有积极的净蛋白质贡献。这是通过反刍动物在牧场上放牧，将低质量的草料转化为高价值的人类可食用蛋白质来实现的。蛋白质生产效率因系统设计而异，土地利用和肠道甲烷排放等其他因素也是生产足迹总体评估中需要考虑的因素。
