Earth has a cow burp problem. (Bigstock)

Earth has a cow problem.

Cows are ruminants. They break down food by fermenting it in a special stomach packed with microbes, then chewing it again. This process lets them get nutrients out of bland, fibrous grass, but it also makes them, ahem, rather gassy. A 2013 report from the Food and Agriculture Organization of the United Nations estimated that 44 percent of the methane — a heat-trapping gas 25 times as potent as carbon dioxide — associated with human activity comes from the global livestock industry. Most of it is released through the animals' front ends.

Let me correct myself: Earth has a cow burp problem.

But atmospheric scientist Luisa Molina and veterinarian Octavio Alonso Castelan-Ortega think they have a solution. In a pilot study conducted at four sites in Mexico, they supplemented cows' diets with plants known to contain bacteria-killing tannins (the same bitter-tasting organic compounds found in coffee and tea). At the right dosage, these tannins disrupt the fermentation of methane-producing methanogens, without interfering with the rest of the cows' digestion. The plants were native to the regions where the study was conducted, so they were easy for farmers to acquire, and in some cases they even made the cows more productive. And they reduced the animals' overall methane emissions by as much as a third.

The research, presented last week at the fall meeting of the American Geophysical Union, signals progress on a weird but very important front in the fight against climate change: the battle against burps.

Other studies have sought to clean up cows' environmentally hazardous belches by mixing special compounds with their feed or engineering supergrass. But Molina and Castelan-Ortega's program has the advantage of being cheap and customizable. It relied on plants that were abundant in the regions where the pilot study was conducted: the cosmos flower (C. bipinnatus) in temperate regions and the tree Leucaena leucocephala in tropical ones. Since locals were familiar with these plants, it was easy and inexpensive to get their cows to graze on them.

The flower reduced methane emissions by about 16 percent, without impacting milk production. Meanwhile, the animals on the L. leucocephala diet not only belched 36 percent less methane, they made more milk in the process.

With further studies, researchers could identify similarly tannin-producing plants native to other farming regions, so that the cows' new low-methane diet could be tailored to where they live.

“If you can select the native plants, that is the best way,” Molina said.

She and Castelan-Ortega estimate that implementing this program across Mexico could save more than a billion kilograms of methane.

The researchers noted that the project is only a pilot study — it has not been published in a peer-reviewed journal or replicated on a bigger scale. But the Mexican government is funding an expansion of the program, and Molina is optimistic about its potential.

Now if she can just teach the cows to say, “Excuse me.”

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