When people burp and fart, it’s considered rude. When cows burp and fart, it contributes to the civilization-threatening trend of climate change.
That’s why scientists at the United States Department of Agriculture (USDA) have been experimenting with new tools—including lasers and a device described as a “breathalyzer for cows”—to figure out how much methane US cattle release into the atmosphere.
Led by Richard Todd, a USDA soil scientist, researchers ran a multi-pronged experiment using these tools and found that the average Oklahoma cow produces about a half-pound of methane gas per day, though those numbers vary with season, diet, soil content, and ecological factors. Todd’s team presented the results at a December meeting of the American Geophysical Union (AGU).
Cows are ruminants, a group of cud-chewing animals that includes sheep, bison, and antelopes. To get the most out of the crops they eat, ruminants regurgitate food and rework it in their mouths with the help of microbes that extract nutrients from plant matter. As a byproduct, these microbes release large amounts of methane gas, which cows eject into the atmosphere and which traps over 30 times more heat than carbon dioxide.
Gassy cattle are far from the major culprit in climate change, but their output—mostly in belch form, although their farts are no joke—is still considerable.
Todd and his colleagues captured cattle emissions using multiple methods, including lasers, GPS trackers, and GreenFeed, a gas detector. Or, if you prefer and as the AGU called GreenFeed in a blog on Wednesday, a bovine breathalyzer.
“Cattle are trained to put their head into an open hood (with food), and while they’re there munching on the little treat the [GreenFeed] device is sampling their breath,” Todd said, according to the AGU blog. “Then we can calculate the methane emissions while they’re inside.”
To get a sense of an entire herd’s output, the team shot open-path lasers above cattle grazing on tallgrass prairies in Oklahoma. These lasers are designed to detect trace gases in the air.
The researchers also measured gas output at sites surrounding the herds, and kept tabs on cows with GPS trackers to create more accurate models of cattle and emissions dispersal. They repeated experiments in summer, autumn, and winter to assess how seasonal changes in forage impacted methane levels.
The number-crunching revealed that the average Oklahoma cow releases about 182 pounds of methane gas per year. That figure is in the same range as a 2018 report by the Australian government that estimated a single cow produces produces 100 kilograms (220 pounds) per year.
A half-pound per day may sound like a small amount. But given that there are nearly 100 million domestic cattle in the USA, those bovine burps add up.
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