California Cows Fail Latest Emissions Test

James Owen
for National Geographic News
August 16, 2005
Standing around chewing the cud, cows don't look especially threatening.
But dairy herds in California are the latest livestock to be branded an
environmental health risk on account of their flatulent behavior.

This month government regulators issued a report identifying dairy cows as the main source of smog-forming pollutants in the San Joaquin Valley, California.

The announcement highlights growing concern over the global impact of greenhouse gases produced by cattle and other livestock.

A dairy cow annually emits almost 20 pounds (9 kilograms) of smog-forming gases known as volatile organic compounds (VOCs)—more than a car or light truck, according to the San Joaquin Valley United Air Pollution Control District.

The local government organization works to monitor and improve regional air quality.

Based on 15 separate studies, the district's figure almost doubles scientists' previous estimate for cow emissions. The finding will form the basis for stricter air quality controls on dairy farms in the area.

The San Joaquin Valley is home to a thriving dairy industry that includes some 2.5 million cattle. With more new dairy operations planned, an additional 400,000 cows are expected to arrive in the valley within the next few years.

But the dairyland is also known for its smog. Over the last six years the valley has violated the federal limit on smog levels more often than any other region in the country.

"The valley air basin harbors some of the worst air quality in the entire country, and on far too many days air quality is unhealthy," said Kelly Hogan Malay of the San Joaquin Valley Air Pollution Control District.

Tailpipe Emissions

Local environmental groups blame air pollution for health problems, such as high rates of childhood asthma, in the region. But dairy farmers say their cows are being made into scapegoats for a gas-guzzling society.

Malay says motor vehicles are a much bigger source of air pollution overall, because they emit pollutants such as nitrous oxides and carbon monoxide in addition to VOCs.

"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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