There are two primary avenues in which raising cattle leads to greenhouse gas emissions:
1. The cattle themselves release methane into the atmosphere
2. Producing & transporting feed for the cattle
Cattle Methane Production Through Digestion
As cattle digest their food (grain or grass), their ruminant digestive systems produce methane, a greenhouse gas. Cattle release this methane primarily by belching, though also to a lesser extent through flatulence.
Studies have shown that grass-fed cattle produce 20% more methane in their lifetime than grain-fed cattle. This is due to two different factors:
1) cattle naturally emit more methane when digesting grass.
2) grass-fed cattle reach market weight more slowly than feedlot cattle, so they’re emitting methane over a longer time (Marshall, 2010).
However, the above percentage may be misleading (from a carbon footprint standpoint) due to a phenomenon known as “carbon sequestration.”
Grass-Fed Cattle & Carbon Sequestration
Grass-fed cattle may mitigate these increased emissions through carbon sequestration. Cattle rotated across pasture land encourage new growth while working manure and other natural fertilizers into the soil.
The theory is that healthy soil traps carbon dioxide, keeping it from rising into the atmosphere. “Indeed, although grass-fed cattle may produce more methane than conventional ones…their net emissions are lower because they help the soil sequester carbon” (Abend, 2010).
Cattle Greenhouse Gasses Due to Grain Feed Production & Transport
Look at the environmental costs of producing feed though, and there’s really no contest. Grass-fed cattle, despite their increased methane production, represent significantly less greenhouse gasses.
The Environmental Cost of Corn
Cattle pasture-raised in a mild climate with rotation between pastures consume food that represents very little greenhouse gas emissions. “Grasses are perennials…that means they grow back year after year and there’s not a lot of fuel used to produce the grasses.” (Gellerman, 2008)
In contrast, the grain (corn) fed to feedlot cattle represents a huge output of fossil-fuel energy. As Michael Pollan (The Omnivores Dilemma) explains: “Much of the carbon footprint of beef comes from growing grain to feed the animals, which requires fossil-fuel-based fertilizers, pesticides, transportation” (Abend, 2010).
Greenhouse gas emissions for all elements of crop production1 have been estimated to vary between 226-426 kilograms of carbon dioxide equivalent2 per metric ton of corn (Adam J. Liska, 2009). That means each pound of corn is responsible for .23lb – .43lb CO2 equivalent greenhouse gasses.
The Feed Emissions Per Head of Cattle
The percentage of corn in cattle feed can vary from feedlot to feedlot, but according to the industry, cattle gain 2.5-4lbs per day on feedlots at a rate of roughly 1lb gained per 6lbs of feed. They also say feed contains an average of 70-90% grain across the industry (The National Cattlemen’s Beef Association) though they aren’t clear how much of that is corn.
From these numbers we can estimate that the average animal consumes 15-24lbs of feed per day. Assuming that at least 70% of that is corn, 2.4-7.2lbs of carbon is released from feed production alone per animal per day.
The industry says that cattle are usually feedlot finished for an average of three to six months (The National Cattlemen’s Beef Association). Based on the “best-case scenario” (an animal eating the minimum feed for the minimum amount of time), the emissions from feeding one animal 15lbs of 70% corn feed for three months are around 201.6lbs of carbon.
How Much Carbon is That?
To put this in perspective, “a medium growth coniferous tree, planted in an urban setting and allowed to grow for 10 years, sequesters 23.3lbs of carbon.” (Environmental Protection Agency, 2011). To offset only the feedlot feed of this “best-case” animal, you need to plant nine trees that live for at least ten years.
33.5 million head of cattle were harvested in the US in 2011 (National Cattlemen’s Beef Association). Grass-fed beef may represent 3% or less of all U.S. beef sales (Cross, 2011). If 32,495,000 of those cattle were fed corn according to the “best case” example above, we’d need to plant at least 292,455,000 trees (living 10 years) to offset the feedlot corn from one year’s worth American grain-fed beef.
Silver Fern cattle are never fed grain of any kind.
1 Fertilizer use & production, lime, herbicides, insecticides, seed, gasoline used, diesel, liquefied gas, electricity, depreciable capital, N2O emissions.
2 Standard greenhouse gas measurement method – an aggregate of all greenhouse gasses emitted, with quantity weighted based on greenhouse impact of the various grasses relative to CO2 (for example, Nitrogen has more effect than CO2, others have less effect than C02)
Abend, L. (2010, January 25). How Cows (Grass-Fed Only) Could Save the Planet. Retrieved July 11, 2011, from Time Magazine: http://www.time.com/time/magazine/article/0,9171,1953692,00.html
Adam J. Liska, H. S. (2009, January 21). Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol. Retrieved December 22, 2011, from DigitalCommons @ University of Nebraska – Lincoln: http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1000&context=ncesrpub
Cross, K. (2011, March 29). The grass-fed vs. grain-fed beef debate. Retrieved December 27, 2011, from CNN.com: http://www.cnn.com/2011/HEALTH/03/29/grass.grain.beef.cookinglight/index.html
Environmental Protection Agency. (2011, November 1). Calculations and References. Retrieved December 27, 2011, from US Environmental Protection Agency: http://www.epa.gov/cleanenergy/energy-resources/refs.html
Gellerman, B. (2008, February 8). Math on the Range. Retrieved July 11, 2011, from Living on Earth: http://www.loe.org/shows/segments.html?programID=08-P13-00006&segmentID=4
Marshall, J. (2010, January 27). Grass-Fed Beef Has Bigger Carbon Footprint. Retrieved July 11, 2011, from Discovery News: http://news.discovery.com/earth/grass-fed-beef-grain.html
National Cattlemen’s Beef Association. (n.d.). Beef Industry Statistics. Retrieved December 27, 2011, from Beef USA – National Cattlemen’s Beef Association: http://www.beefusa.org/beefindustrystatistics.aspx
The National Cattlemen’s Beef Association. (n.d.). Fact Sheet: Feedlot Finishing Cattle. Retrieved December 27, 2011, from Beef USA – National Cattlemen’s Beef Association: http://www.beefusa.org/uDocs/Feedlot%20finishing%20fact%20sheet%20FINAL_4%2026%2006.pdf
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