This study compared the environmental impact of conventional, natural and grass-fed beef production systems. A deterministic model based on the metabolism and nutrient requirements of the beef population was used to quantify resource inputs and waste outputs per 1.0 × 10kg of hot carcass weight beef in conventional (CON), natural (NAT) and grass-fed (GFD) production systems. Production systems were modeled using characteristic management practices, population dynamics and production data from U.S. beef production systems. Increased productivity (slaughter weight and growth rate) in the CON system reduced the cattle population size required to produce 1.0 × 10kg of beef compared to the NAT or GFD system. The CON system required 56.3% of the animals, 24.8% of the water, 55.3% of the land and 71.4% of the fossil fuel energy required to produce 1.0 × 10kg of beef compared to the GFD system. The carbon footprint per 1.0 × 10kg of beef was lowest in the CON system (15,989 × 10t), intermediate in the NAT system (18,772 × 10t) and highest in the GFD system (26,785 × 10t). The challenge to the U.S beef industry is to communicate differences in system environmental impacts to facilitate informed dietary choice. View Full-Text