California Cows Fail Latest Emissions Test

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"The reason VOCs are a concern at all is because they're one of the components that contributes to the formation of ozone, which is the primary ingredient of smog," Malay said.

But VOCs aren't the only worrisome gases that emanate from livestock. Scientists say animals such as cattle and sheep are responsible for around 20 percent of global methane emissions.

Methane, a greenhouse gas, is believed to be a major driver of climate change, because it traps 21 times as much heat in the atmosphere as carbon dioxide.

"In more rural communities as much as 50 percent of the methane comes from livestock," said Jamie Newbold, professor at the Institute of Rural Sciences in Aberystwyth, Wales.

Newbold is among a growing number of scientists now investigating how farm animals influence atmospheric pollution. The field is sometimes dismissed by critics as "fart science."

"Actually it's belching, not farting, that's the problem," Newbold said. "A full-grown dairy cow can belch 400 to 500 liters [106 to 132 gallons] of methane a day."

Microbes in the animals' stomachs help ferment grass and other foods into a digestible state, producing the offending gases.

"The fermentation vessel of a dairy cow is around 100 liters [26 gallons]," Newbold said.

Humans have a far more limited capacity. When people produce methane, it's only a matter of teaspoons (milliliters), Newbold notes.

"Humans don't have that active microbial fermentation. It's to do with having a grass diet," he said.

In New Zealand, home to around 40 million sheep and 10 million cows, 43 percent of the nation's greenhouse gas contributions come from livestock, scientists say.

In Canada livestock are reckoned to produce about one percent of global methane emissions.

Escaping Profits

Such emissions aren't bad just for the environment—livestock farmers are seeing potential profits escape into thin air.

Animals that put their energies into making gas are less efficient at producing milk and meat. Fodders that limit gas emissions in cattle and sheep should make the animals more economical to farm.

"Animals under these situations become more efficient at converting feed into lean tissue or milk protein," said Karin Wittenberg, a professor of animal science at the University of Manitoba in Canada.

Researchers are currently developing a range of anti-flatulence aids. Belgian scientists found that adding certain fish oils to a sheep's diet can cut belching by almost half.

Elsewhere, Australian researchers have created a vaccine that inhibits gas-producing microbes in a sheep's gut. And high-grade alfalfa grass pastures have been found to reduce windy side effects in grazing cows.

Newbold's group at the Institute of Rural Sciences in Wales has worked to produce organic acids to prevent methane buildup in cow stomachs.

"The hope is that many of these additives will be cost-effective for farmers, because they minimize the amount of energy an animal loses through methane production," Newbold said.

"Cattle and livestock are only part of the problem," he added. "There are a lot more greenhouse gases that are produced by cars than cattle. But [cattle] do make a contribution, and they should be a part of the solution."

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