By Ned Rozell

Scientists measure a cow’s respiration at a lab in Toluca, Mexico. Photo by Octavio Castelán-Ortega.

Many creatures, including you and me, emit methane from time to time. Microbes within our guts break down one substance and turn it into another, making methane in the process. Northern lakes and tundra plants also leak methane. That gas, too, is from microbes, which become more active as the air warms.

Scientists study methane because of its ability to warm the world — methane is 28 times more potent than carbon dioxide as a greenhouse gas.

Because of this, a number of scientists at a recent conference showed their work on finding manmade sources of methane, from electronically sniffing manhole covers in Cincinnati to sampling the emissions from cows in Mexico.

Cows are one of the largest sources of man-caused methane. Livestock around the world contribute 44 percent to methane emissions attributable to the actions of humans, according to a report from United Nations researchers.

There are a lot of cows out there. More than 90 million in the U.S., most of them in Texas, Nebraska, Kansas and California. Alaska is way down on the list, home to about 14,000 cows.

There are about 33 million cattle in Mexico, where a few scientists are experimenting to concoct a cow diet that will reduce methane emissions.

Like moose, cattle are ruminants that break down their food by fermentation. This process, which also makes them gassy, allows them to pull nutrients from food as bland and fibrous as grass, and in the moose’s case, willow twigs and buds. Cows that eat corn and wheat produce less methane than grass-fed beef.

This may come as a surprise, but 90 percent of cow methane comes from their front ends. Octavio Castelán-Ortega measured that in an experiment he and others conducted in Mexico. He works at the Autonomous University of Mexico State in Toluca, near Mexico City.

Castelán-Ortega, a veterinarian, and Luisa Molina, an atmospheric scientist, monitored the respiration of cows and found steep reductions in methane when cows were fed a diet enhanced with certain plants. They presented their results in an eye-catching poster (featuring a cow with its head in a chamber that resembled a voting booth) at the recent fall meeting of the American Geophysical Union in San Francisco.

In a study at four sites in Mexico, Castelán-Ortega and Molina found cows that fed on grasses mixed with the leaves of delicate tropical leucaena trees belched about 36 percent less methane than those on a straight grass diet. The cosmos flower, with the Latin name Cosmos bipinnatus, reduced methane emissions 26 percent when it was added to feed.

The diet including leucaena tree leaves also improved the cows’ milk production. Both plants contain bacteria-killing tannins that disrupt fermentation without interfering with a cow’s digestion. Too much of the plants would be toxic, but a small proportion seems to be beneficial. We drink tannins all the time. They are the bitter compounds in coffee and tea.

The Mexico study was a pilot project using plants from the tropics and other warm regions. Castelán-Ortega said researchers could identify and test tannin-containing plants from cooler climates. A small tweak in diet could result in a big reduction in greenhouse gases from the world’s growing population of cows.

Meanwhile, here in Alaska, methane wafts freely from 950,000 caribou, 200,000 moose, and thousands of sheep and goats.

Ned Rozell is a science writer for the University of Alaska Fairbanks‘ Geophysical Institute. Since the late 1970s, the Geophysical Institute as provided this column free in cooperation with the UAF research community. More of Ned’s columns can be found here.

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