How better-fed cows could cool the planet

When cows digest, they burp methane gas, a powerful greenhouse agent. Scientists are working to try to reduce that.

By Bettina Gartner | Contributor to The Christian Science Monitor

from the August 16, 2007 edition

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It may be bad manners, but it's also necessary: Every 40 seconds or so, a cow burps. Scientists are now scrambling to make them burp less – not to make more polite cows, but a cooler planet.

As cows digest their food (up to 150 pounds of grass, hay, and silage per day, along with 20 pounds of concentrated feed), myriad microorganisms – bacteria, protozoa, fungi, and archaea – busily break down the fibers and other nutrients in their rumens. In the process, hydrogen and carbon dioxide are released. The archaea (a kind of bacteria) transform the two gases into methane (CH4), up to 100 gallons of it per cow per day, and the cows get rid of it mainly by burping.

How could a burp matter? But it does.

Odorless, colorless methane – the primary of natural gas – is a powerful greenhouse agent. According to the US Environmental Protection Agency, pound for pound methane is about 21 times more effective at warming Earth's atmosphere than carbon dioxide is. Globally, ruminant livestock – including cattle, goats, and buffaloes – produce about 80 million metric tons of methane a year, accounting for about 28 percent of man-made methane emissions annually.

Recently, researchers from the Japanese National Institute of Livestock and Grassland Science in Tsukuba calculated the environmental impact of a serving of beef and published the result in The New Scientist. According to them, the production of one kilogram of beef (2.2 pounds) results in the emission of greenhouse gases with a warming potential equivalent to 80 pounds of carbon dioxide. In other words: Serving steak to your family is the greenhouse-gas equivalent of driving 155 miles.

What's a cow to do?

As the demand for meat steadily rises globally, the question is how can we keep cows from burping.

British researchers have begun a $1.5 million government research program to propose ways to change cows' diets in order to reduce methane production by feeding them grasses with higher levels of sugar, which facilitate digestion. "These grasses present a better balance of nutrients to the microbial population in the rumen and are used more efficiently," says Prof. Mike Theodorou, head of the UK's Science Development at the Institute of Grassland and Environmental Research in Aberystwyth. "In doing so, more of the ingested carbon and nitrogen will be converted to meat, milk, hide, and wool."

The scientists are investigating how such plants can be bred to contain even higher sugar content and to grow more abundantly on pastureland.

Other researchers suggest adding certain plant ingredients to livestock menus. Michael Kreuzer, head of the Swiss Ruminant Nutrition Group in the Institute of Animal Science of ETH Zurich, proposes adding extra fat (from coconuts, crushed flaxseed, or sunflower seed), as well as extracts rich in tannins and saponins (already available in powdered form).

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