Grazing or confining — Decoding Beef's environmental footprint

Greenhouse gas (GHG) emissions of beef production are extremely variable depending on the livestock production system (LPS) used, with lack of clarity on the influencing factors. Here, we assess those factors using a mass balance model with regional case study data for Portugal. We show that the whole-system GHG emissions range for beef production from steers in beef herds is 15–124 kg CO 2 e per 100 g protein depending on LPS (confined, pasture-based or mixed), breed, age at slaughter, and adequacy and upstream impact of supplemental feed. If steers are adequately supplemented, then LPS that involve at least a stage of grazing for steers have the lowest emissions, regardless of supplemental feed impact. In case of suboptimal supplementation during grazing, confinement is optimal at intermediate to low feed impact. For high feed impact, slaughtering at weaning is optimal. Choosing the best LPS and slaughtering age reduces the range of emissions to 15–35 kg CO 2 e per 100 g protein. • We aimed to understand why greenhouse gas emissions of beef can be so variable. • Beef can be produced using many different production systems, breeds and feeds. • If steers are adequately fed, grazing systems produce beef with low emissions. • Confined systems may be optimal if steers are under-fed and feed emissions are low. • Slow and fast-growth breeds are equally likely to produce low emissions beef.