Study: Cattle on high-roughage diets emit more greenhouse gasses

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Scientists have long known that cattle produce carbon dioxide and methane throughout their lives, but a new study pinpoints the cow-calf stage as a major contributor of greenhouse gases during beef production.

In a new paper for the Journal of Animal Science, scientists estimate greenhouse gas emissions from beef cattle during different stages of life. They show that, depending on which production system farmers used, beef production has a carbon footprint ranging from 10.7 to 22.6 kg of carbon dioxide equivalent per kg of hot carcass weight.

According to study co-author Frank Mitloehner, an associate professor in the Department of Animal Science at UC Davis, one source of greenhouse gases was surprising.

“If you look at everything that contributes to greenhouse gases through the beef supply chain, then it is the cow-calf that produces the greatest greenhouse gases,” Mitloehner said.

In the cow-calf phase, the cow gives birth and nurses the calf until the calf is six to 10 months old. During this time, the cow eats rough plants like hay and grasses. The methane-producing bacteria in the cow’s gut thrive on these plants.

“The more roughage is in the diet of the ruminant animal, the more methane is produced by the microbes in the gut of the ruminant, and methane comes out the front end,” Mitloehner said.

In feedlots, by contrast, cattle eat mostly corn and grains, which the methane-producing bacteria cannot use as effectively.

Methane is one of the most important greenhouse gases. Methane has a greater capacity to trap heat in the atmosphere than carbon dioxide.

The beef industry has been paying close attention to greenhouse gas emissions in recent years.

“We are doing a lot to measure and mitigate our impact,” said Chase Adams, director of communications for the National Cattlemen’s Beef Association.

In a 2011 paper for the Journal of Animal Science, researcher Jude Capper showed that the beef industry today uses significantly less water and land than 30 years ago. The industry has also reduced its carbon footprint by 16.3 percent per billion kilograms of beef produced.

According to Mitloehner, beef producers can further reduce their carbon impact by using new technologies like growth promotants. However, consumers are often uncomfortable with these methods, and they choose organic beef or beef with reduced amounts of growth promotants.

“The technologies many consumers are critical of are those that help us receive the greatest environmental gains,” Mitloehner said.

The study by Mitloehner and his colleagues is titled “Carbon footprint and ammonia emissions of California beef production systems.” It can be read in full at the Journal of Animal Science website.

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NCMT  |  January, 31, 2013 at 09:21 AM

So this suggestes that "grass fed/fat" would cause even more GhG?! Seems these are the same folks that want it both ways.

D. B.    
TX  |  January, 31, 2013 at 09:46 AM

Grass fed are slaughtered at 750-800#, the weight most grain fed enter the feedlot, for an additional 400# of gain on grain based rations. What is questionable is to lose the 1/3 more possible production from that one animal thru the feeding stage when we choose not to feed them further, slaughter off grass. It takes more grass fed calves to produce the same amount of product you can get from one thru grain feeding. That means more cows and calves are needed to get that same volume of product from them. I would say, there is where you get the extra methane in grass fed, compared with grain fed.

January, 31, 2013 at 12:37 PM

Has anyone ever stopped to think of the number of Elk and Bison that would displace the cattle if we were to eliminate domestic cattle? How much methane do Elk and Bison put into the atmosphere? What mechanisms pull methane back out of the atmosphere? Someone, with good science, needs to answer these questions before suggesting that we quit producing cattle.

iowa  |  January, 31, 2013 at 12:54 PM

EXCELLENT point Bt! I remember in history the Indians claimed that herds would sometimes take weeks to pass. In less than200 years the Bison population has increased from a little over 500 to more than half a million. Considering that conservative estimates put the bison in North America more than 5000 years ago and at the growth rates the bison population was far larger than any cattle population. I mean think of it. The cattle population is 90 million. Bison numbers almost extinct, in 200 years, have grown to half a million. What would they do in 5000 years? So the greenhouse gas of cattle is nowhere near what the bison produced historically. Hey maybe that is why it was warmer in the middle ages than it is now. Bison farts!

January, 31, 2013 at 04:18 PM

Seems like vegetarians would cause more greenhouse gasses also. So the millions of people on this earth add significantly to the greenhouse gas problem.

MN  |  January, 31, 2013 at 07:57 PM

The process of digesting roughages in the rumen generates more methane than digestion of starch. Secondly, feedlot rations are carefully balanced to meet an animal's needs. That is difficult to do in a grazing situation. Unbalanced diets produce more methane. Almost all feedlot rations include an ionophore which makes the digestive process more efficient and dramatically reduces methane emissions. It is difficult and expensive to get an ionophore into grazing cattle but the methane reduction would be significant. I don't think any ruminant nutritionists were surprised by these findings.

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