New Zealand Tries to Cap Gaseous Sheep Burps

By John Roach
for National Geographic News
May 13, 2002
New Zealand scientists trying to curb their country's influence on global warming may have found an answer to belch about: Livestock that eat plants high in condensed tannins produce up to 16 percent less methane, a potent greenhouse gas.

Tannins are the yellow-brown chemical compounds found in many plants and give red wine its distinctive flavor.

Methane is one of the three most potent gases that some scientists say are causing the Earth to warm up at an accelerated and unnatural rate. Carbon dioxide from the burning of fossil fuels is the most common greenhouse gas in the world.

"New Zealand is unique in that over 50 percent of its greenhouse gas emissions arise from methane released by enteric fermentation," said Katharine Hayhoe, an atmospheric scientist at the University of Illinois, Urbana-Champaign, Illinois.

Enteric fermentation is methane produced as part of the normal digestive process of animals, such as cows and sheep. It is primarily released in the form of burps.

The 45 million sheep and 10 million cattle in New Zealand make for a lot of burped methane—about 90 percent of that country's methane emissions, according to government figures.

For comparison, livestock are responsible for about 2 percent of the United States' greenhouse gas emissions, according to the U.S. Environmental Protection Agency.

Protocol Preparation

New Zealand plans to sign the Kyoto Protocol, an international treaty to combat global warming, this August. Under the treaty, the country must reduce its greenhouse gas emissions to 5.2 percent below 1990 levels by 2012.

Thus, any step that can be taken to reduce the impact livestock have on global warming would certainly be welcome, say researchers at AgResearch Grasslands in Palmerston North, New Zealand.

Although livestock are exempt from a tax plan unveiled by the New Zealand government in April to help meet its targets under the protocol, the agriculture industry is required to fund research on ways to reduce agriculture methane emissions.

At news of the plan, AgResearch Grasslands said it is already on the job.

Agricultural researchers have long known that livestock fed certain plants produce less methane, but until now they did not know what it is about those plants that cause the desired effect.

To find out, they put a halter contraption over a cow named Myrtle. A little vacuum hose rests above her nose and a vessel around her neck collects methane emissions for 24-hour periods. Different food fed to Myrtle gets different results.

Analysis of the results indicates that the condensed tannins found in certain pasture species, such as legume lotus, are responsible for the reduction.

"It's early days, but this is very encouraging news that will give our research new impetus and offer positive opportunities to New Zealand farmers for controlling this problem," said Michael Tavendale, one of the researchers who made the discovery, in a statement.

The next steps in the research include developing strategies where diets containing condensed tannins can be used to lower livestock methane emissions, for example by using more species such as legume lotus as feed or introducing the tannin component into other pasture species.

Condensed tannins have other benefits too, say the researchers. They can improve milk yields, increase livestock weight gain, decrease parasite burden and reduce occurrence of bloat.

True Targets

To put this research and methane production by cattle into perspective, AgResearch Grasslands says that the average New Zealand dairy cow produces about 198 pounds (90 kilograms) of methane per year, which is equivalent in energy to 32 gallons (120 liters) of gasoline.

So, for a 200-cow dairy herd the "petrol equivalents" are 6,400 gallons (24,000 liters) of gasoline, or enough gas to drive an average vehicle 124,274 miles (200,000 kilometers), say the researchers.

Thus, is this research an effective way to combat global warming?

"Certainly," says Hayhoe. "However, the global impact of this method is limited since 65 percent of global warming is entirely due to fossil fuel burning."

"There is no question that any long-term efforts to address climate change must involve steps to eventually eliminate carbon dioxide emissions from fossil fuels through efficiency increases, carbon sequestration, and increasing reliance on alternative energy sources."

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