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The grass is always greener… or is it?

by Jude L. Capper, Ph.D., Assistant Professor of Dairy Sciences – Washington State University

Summary

Productivity (meat yield and/or growth rate) is a major component of reduced environmental impact and is optimized in conventional (corn-fed) beef production systems. Nonetheless, corn-fed finishing systems are often claimed to be less environmentally sustainable than finishing cattle on pasture.

A partial life-cycle assessment (LCA) was conducted to quantify the environmental impact of corn-fed vs. grass-fed beef. According to the LCA, finishing steers fed conventional corn diets had increased growth rates and reduced days on feed compared to their grass-finished compatriots. To produce a comparable amount of beef, energy use was 2.5 times higher, methane emissions were increased 2.8 times and land use was 12.6 times higher in grass-fed finishing systems.

To accurately assess the environmental impact of livestock production systems, it is essential to rely on sound science rather than assuming that the intuitive solution is correct. 

Introduction

Livestock farmers and ranchers face an ever-increasing challenge in producing sufficient high-quality, nutritious, affordable meat to fulfill the need of a growing population. The environmental impact of livestock production looms like a specter over current food discussions, with myriad “authorities” (ranging from the media and celebrities to pseudo-legitimate anti-animal agriculture groups) advising consumers that a vegetarian or vegan lifestyle is the best choice for the environmentally conscious consumer. The United Nations’ Food and Agriculture Organization’s finding that worldwide livestock production contributes 18 percent of total global greenhouse gases (GHGs) is often used to back-up the statement, despite the fact that livestock production only contributes less than 3 percent of U.S. GHG emissions. Nonetheless, a preponderance of self-proclaimed experts with no background in food production advocate grass-fed beef as being more environmentally sustainable than conventional (corn-fed) beef. With this in mind, a partial LCA approach was used to quantify the environmental impact of cornfed vs. grass-finished beef. 

Discussion

Improving productivity (output per unit of resource input) is key to reducing the environmental impact of livestock production. If milk yield, meat yield or growth rate can be increased, fewer resources are required to produce the same amount of food. For example, average beef-carcass yield per animal has increased over the past 30 years from 586 pounds in 1975 compared to 774 pounds in 2007, which, in combination with reduced time to slaughter over the same time period (19 months vs. 18 months), reduces resource use per unit of meat. Time to slaughter is primarily affected by growth rate, thus this is a primary productivity measure by which to mitigate the environmental impact of meat production.

Approximately 50 percent to 75 percent of a conventionally-reared beef animal’s life is spent on pasture; significant feed (corn) inputs are only used during the finishing period at the feedlot. By contrast, certified grass-finished beef animals are finished on pasture without supplemental corn feed. If we take a superficial view that considers only the energy inputs required to produce and harvest corn in conventional systems compared to the animals “harvesting” the pasture through grazing, the idea that grass-finished beef has a lower environmental impact appears to be correct. However, this suggestion relies on the three erroneous assumptions, that animals within both systems: (1) have equal energy requirements, (2) take the same time to finish, and (3) produce the same quantities of GHGs from enteric fermentation.



As shown in Figure 1, beef steers finished on pasture have an additional energy requirement for grazing activity, thus increasing total daily maintenance energy requirements. The growth rate of steers on pasture is also lower than that of steers fed corn. This increases the length of the finishing period, each day of which incurs a maintenance cost, which must be accounted for total environmental impact. Finally, grassbased diets promote greater ruminal acetic acid production, increasing enteric methane production. As with all LCAs, environmental impact should be expressed per unit of food produced, i.e. energy use, methane output and land use per pound of beef. As the data in Figures 1 and 2 clearly demonstrate, energy use is 2.5 times higher, methane output is 2.8 times higher and land use is 12.6 times higher in grass-finished systems compared to cornfed systems.



It should be noted that this example is intended to demonstrate the impact of improved productivity – the growth rates are those predicted by the National Research Council (NRC) for corn-fed vs. grass-finished animals and will vary between individual production systems. Previous commentators on this data have noted that grass-finished beef animals are often finished at a lower slaughter weight than conventional animals. While this is undoubtedly true, it conveniently omits a key point. The beef industry does not exist to produce a set number of finished animals, but to provide sufficient beef to fulfill consumer requirements. For example, if grass-finished steers are slaughtered at 1,100 pounds (each animal requiring two times the energy for finishing compared to 1,400 pound corn-fed animals), beef production per animal is cut by 21 percent. To produce a comparable amount of beef, 1.27 grass-finished steers are therefore required to replace each corn-fed steer. Not only does this increase resources (energy, land) and GHG emissions from finishing, but also increases the size of the national beef cow herd – each cow requiring feed resources and emitting GHGs. The need to feed the growing population is constantly ignored in the discussions propounded by people such as “Food, Inc.” director Robert Kenner, author Michael Pollan and others in favor of “low-input” systems. 

Conclusions

Extensive rangeland systems provide sufficient nutrients to support the cow-calf component of the U.S. beef production system and the use of pasture in this manner doubles the amount of land available for food production. However, resource (energy and land) and methane emissions are considerably reduced in corn-fed finishing systems compared to grass-finished systems. The contrast between the sustainability of pasture for cow-calf compared to finishing systems underlines the importance of tailoring the system requirements to the resources available. The increases in resource use per unit of output associated with grass-finished beef production systems demonstrate that the popular perception of “sustainable” systems is very much at odds with the true picture. 

Additional Resources

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Capper, J. L., E. Castañeda-Gutiérrez, R. A. Cady, and D. E. Bauman. 2008. The environmental impact of recombinant bovine somatotropin (rbST) use in dairy production. Proceedings of the National Academy of Sciences 105: 9668-9673. 

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