Summary
In order to sustain the current demand for cattle, a 67% increase in cattle on grass-finishing lots and more pasture land would be needed to support a switch to purely grass-fed beef. This is due to grass-fed cattle taking longer to reach slaughter weight. This would result in high methane emissions. One limitation is the use of cattle population data from 2012 and 2013, which most likely differs to the cattle population at time of publication. A strength of this study is considering factors that could influence the decision to switch to grass-fed beef such as animal welfare and production cost. This study suggests that purely grass-fed beef is unsustainable in terms of meeting supply and demand and the increase in methane that would occur.
In the US, there is growing interest in producing more beef from cattle raised in exclusively
pasture-based systems, rather than grain-finishing feedlot systems, due to the perception that it is
more environmentally sustainable. Yet existing understanding of the environmental impacts of
exclusively pasture-based systems is limited by a lack of clarity about cattle herd dynamics. We model
a nationwide transition from grain- to grass-finishing systems using demographics of present-day
beef cattle. In order to produce the same quantity of beef as the present-day system, we find that a
nationwide shift to exclusively grass-fed beef would require increasing the national cattle herd from 77
to 100 million cattle, an increase of 30%. We also find that the current pastureland grass resource can
support only 27% of the current beef supply (27 million cattle), an amount 30% smaller than prior
estimates. If grass-fed systems include cropland-raised forage, a definition that conforms to typical
grass-fed certifications, these supplemental feeds can support an additional 34 million cattle to
produce up to 61% of the current beef supply. Given the potential of forage feed croplands to
compete with human food crop production, more work is required to determine optimal agricultural
land uses. Future US demand in an entirely grass-and forage-raised beef scenario can only be met
domestically if beef consumption is reduced, due to higher prices or other factors. If beef
consumption is not reduced and is instead satisfied by greater imports of grass-fed beef, a switch to
purely grass-fed systems would likely result in higher environmental costs, including higher overall
methane emissions. Thus, only reductions in beef consumption can guarantee reductions in the
environmental impact of US food systems.