With most of the attention on cutting greenhouse gas emissions from things like cars and power plants, we often overlook an odiferous offender: cow burps. Belching from ruminants, which include cows, sheep, and goats, releases methane, which is a greenhouse gas that can dramatically trap more heat than carbon dioxide (CO2). Over a 100-year period, methane’s heating trapping potential is 25 times greater than CO2’s potential!

According to the EPA, livestock farming of ruminants produces methane to the tune of about 80 million metric tons annually, which is roughly “28% of global methane emissions from human-related activities. An adult cow may be a very small source by itself, emitting only 80-110 kgs of methane, but with about 100 million cattle in the U.S. and 1.2 billion large ruminants in the world, ruminants are one of the largest methane sources.” This is supported by a Food and Agriculture Organization study, which concluded that livestock farming accounts for 18% of global greenhouse gas emissions. In contrast, the same study found that vehicles account for only 13% of global greenhouse gasses, the majority of which is CO2.

Ruminant Digestion

The source of the methane is actually microbes found in the cattle’s rumen, the cow’s “grass fermenting tank.” Cows and other ruminants lack enzymes that break down fiber (cellulose) found in grass and, therefore, depend on microbes to digest it through fermentation. One of the byproducts of this process is methane. While most of the methane is released by burping or rising from manure, some of the gas is also passed when ruminants “break wind.”

These facts have spurred scientists and cattle farmers to try and cut greenhouse gas emissions by adjusting the cows’ diet:

Another way to dramatically reduce methane emissions, as suggested last week in a Freakonomics podcast, is to switch from a cow-centric to a kangaroo-centric diet–an idea that has been bloated around before.

“You could also switch from eating beef to eating kangaroo — because kangaroo farts, as fate would have it, don’t contain methane. But just imagine the marketing campaign that would be needed to get Americans to take up ’roo-burgers. And think how hard the cattle ranchers would lobby Washington to ban kangaroo meat. Fortunately, a team of Australian scientists is attacking this problem from the opposite direction, trying to replicate the digestive bacteria in kangaroos’ stomachs so it can be transplanted to cows.” [links added by me]

Someone should tell the Freakonomics guys that Eight Mile Creek in New York has been serving kangaroo since 2010. Apparently, kangaroo meat is very lean and tastes “just like sweet filet mignon.” [h/t @brainofrich]

‘Roo meat

As it turns out, however, marsupial farts DO contain methane. In a recent study, red-necked (refraining from red neck jokes) wallabies were housed in special respiration chambers that had air constantly pumped in, which allowed the researchers to measure the amount of methane coming out of the chamber. The wallabies produced between 25-33% of the expected amount of methane that would be produced by ruminants fed the same diet. “Based on the uneven release of CH4 with time” the researchers concluded that the gas mainly came from farting rather than breathing, which would have produced a constant stream of methane. The drop in methane production could be due to the presence of certain gut bacteria that can help break down plant matter without making methane.

One friend, however, pointed out that kangaroos are much smaller than cows. Given the size difference, how much feed would be required and, consequently, how much methane would be produced in order to get an equivalent amount of kangaroo meat? Might the methane “savings” be a wash? While another friend suggested, “They’ve got this all wrong, you put a balloon on the cow’s ass, collect methane, and then burn it for energy. Yes this really happens.” Ask and you shall receive:

Related Reading and Videos:

‘Gas-less’ kangaroo secret sniffed out

Dinosaur gases ‘warmed the Earth’ (bbc.co.uk)

China’s emissions estimates don’t add up

Tackling belching cows (Video)


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