Some cows become steaks. Others star in TV commercials. Lucy, a 5-year-old Black Angus, has been recruited for an experiment to fight global warming.
Lucy is a resident of the beef pen at Washington State University's Pullman campus, grazing away the spring days, chewing her cud and burping into a tube that directs her breath into a canister slung around her neck.
She is one of several cows helping chemist Halvor Westberg and his colleagues analyze greenhouse gas emissions. The work can be messy and unglamorous. It sometimes degenerates into a shoving match between man and beast as Westberg struggles to attach the monitoring equipment to the balky bovines.
Yet the research plays a key role in supplementing computer models and laboratory experiments with real-world findings about livestock and their effect on climate change.
"To understand how to reduce greenhouse gases in the world, you have to understand the sources," Westberg said.
Like cows the world over, Lucy is a prodigious source of methane, a major constituent of greenhouse gases. Chewing away, she is a picture of benign passivity. But the inner Lucy is a fermentation factory. The more she chews, the more she belches molecules of methane that float into the sky and trap the sun's heat.
While emissions from power plants, auto tailpipes and forest fires have long been blamed for warming the planet, the innards of livestock, including sheep and goats, are now being recognized as significant contributors as well.
Methane concentrations in the atmosphere have more than doubled in the last century, with cattle accounting for nearly 20% of the pollutant, scientists say.
"I know it sounds crazy, but it's a serious topic," said Ralph Cicerone, an atmospheric scientist and chancellor at UC Irvine. "Methane is the second-most-important greenhouse gas in the atmosphere now. The population of beef cattle and dairy cattle has grown so much that methane from cows now is big. This is not a trivial issue."
The world's cattle herds number about 1.3 billion animals -- more than double the number 30 years ago. There are also 1.1 billion sheep and goats. In the United States, cattle have become so numerous that there are two animals for every five people. California and Texas have the most dairy and beef cattle. The Environmental Protection Agency estimates that 25% of the nation's methane emissions come from livestock.
In eastern Washington, Scotland, New Zealand and Australia, feedlots and pastures are becoming laboratories for researchers testing an assortment of potential remedies for livestock greenhouse gas. They are experimenting with vaccines, reformulated feed, selective breeding and bioengineered cows.
In the cattle pen at Washington State, Lucy's role is to help scientists get more accurate measurements of cow gas. Each evening, Westberg checks to see how much of it the animal has belched into the small container around her neck.
Experiments like this are being tried worldwide to test cattle in varying environments and eating different diets. The information could help produce ways to reduce the methane generated by livestock.
Such research is driven in part by the 1997 Kyoto accord, which calls on industrialized countries to reduce their greenhouse emissions. The United States withdrew from the treaty in 2001, but 180 other nations have endorsed it.
Despite the evidence, reports that cows can cook the planet are not always taken seriously. Researchers at Washington State and elsewhere complain they have become the Rodney Dangerfields of science, their work reduced to punch lines on late-night TV and comedy club acts.
Lampooning research on livestock flatulence is a staple for nationally syndicated columnist Dave Barry. One Wisconsin politician recently ran for Congress campaigning against such research as a waste of government funds.
"People like to make jokes about it. People say it's wasting government money ... but global climate change is not a laughing matter," said Lowry A. Harper, a research scientist at the U.S. Department of Agriculture.
The key to understanding the problem is knowing which end of the cow is responsible. About 95% of the gas originates, not as flatulence, but as exhalation. It is the unwanted byproduct of a unique digestive system that has made cattle engines of agricultural production, but also prodigious belchers.
Cows lived in harmony with the atmosphere for thousands of years. Then humans developed a taste for the animals and their dairy products, and nature's equilibrium was disturbed. Simple barnyard creatures were transformed into agents of climate change, not by their own doing, but because people dramatically multiplied their numbers so they would produce more milk, cheese and meat.
Methane comes from a variety of sources, including coal mining, rice paddies and wetlands. Human activities produce about two-thirds of the gas. Methane accounts for about 20% of planetary warming, studies show.