A new study finds that feeding seaweed pellets to grazing beef cattle dramatically reduces their greenhouse gas emissions
Sarah Kuta December 3, 2024 4:58 p.m.
Cows are a gassy bunch. As they stand in fields and munch on grass, the animals burp and fart—and, in doing so, they release billions of pounds of heat-trapping methane gas into the atmosphere. In total, the livestock industry is responsible for between 11.1 and 19.6 percent of global greenhouse gas emissions, and cow belching is the biggest contributor to that number.
Now, another study is pointing the way toward an emerging solution: seaweed pellets.
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When grazing beef cattle were fed seaweed supplements, their methane emissions dropped by nearly 40 percent. And this change in diet had no apparent effects on the animals’ weight or health, researchers report in a new study published Monday in the journal Proceedings of the National Academy of Sciences.
Previous research has shown that seaweed helps cut methane emissions in feedlot cattle and dairy cows. But the new paper is the first to demonstrate the effects among grazing beef cattle, which produce more methane than feedlot cattle and dairy cows because of the high fiber content of the grass they eat.
To test the effects of seaweed, scientists conducted a ten-week experiment at Matador Ranch in Dillon, Montana. They divided 24 young, neutered, male beef steers—which were a mix of Angus and Wagyu breeds—into two groups. While the cattle were grazing in fields, researchers offered one group pellets containing seaweed (Asparagopsis taxiformis), which the steers ate voluntarily. Researchers dispensed the pellets using solar-powered machines that also measured how much methane the cows produced. The other group of cattle did not have access to the seaweed pellets.
The seaweed-eating group produced 37.7 percent less methane, on average, than the control group did. “Considering the substantial contribution of ruminant livestock to global greenhouse gas emissions… this research offers a promising avenue for mitigating climate change,” according to the paper.
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In the real world, farmers and ranchers have different options for serving seaweed to their grazing cattle. They could offer them pellets, just like the researchers did in the study, or they could provide a seaweed-infused “lick block,” a small cube farmers set out so that their livestock get all the salt and minerals they need to thrive.
As it stands now, ranchers already supplement the diets of their grazing cattle during winters or when grass is not available—so incorporating seaweed should be relatively straightforward, researchers say.
“This method paves the way to make a seaweed supplement easily available to grazing animals,” says study co-author Ermias Kebreab, an animal scientist at the University of California, Davis, in a statement.
Cow farts and burps both release methane into the atmosphere. But the burps are the worst offenders, responsible for producing the majority of cattle-emitted methane, according to NASA.
Why do cows belch up so much methane? The answer lies in their unique anatomy. Cattle are ruminants, a type of mammal that has four stomach chambers to help with digesting high-fiber foods. When they take a bite of grass and swallow, the fibrous plant matter enters the first stomach chamber, called the rumen.
Inside the rumen, microbes break down the sugars in the grass via fermentation, a process that creates methane as a byproduct. This causes cows to burp, which sends the methane into the atmosphere.
Seaweed, meanwhile, contains a compound called bromoform that blocks methane-producing enzymes in the rumen. This, in turn, reduces the amount of methane cows burp up.
Earlier studies have found that seaweed can help reduce methane emissions by up to 82 percent in feedlot cattle and more than 50 percent in dairy cows.
Researchers in Oregon are currently working on a similar experiment that also involves beef cattle. Their project is focused on cows that graze in sagebrush-steppe ecosystems and uses a different type of seaweed, called Pacific dulse, which is grown commercially on the state’s coast.
Scientists involved in the Oregon study plan to feed varying amounts of seaweed to cattle, then track any corresponding changes to their methane outputs. They also plan to measure carbon levels in the soil. Their experiment will last five years and is being funded by the U.S. Department of Agriculture.
“Our final and major goal is to be able to come up with some strategy for producers,” says Juliana Ranches, an agricultural researcher at Oregon State University, to Oregon Public Broadcasting’s Alejandro Figueroa. “[To say] ‘hey, here’s the seaweed. It really works, you need to feed it this amount. Here’s how we’re going to suggest you feed it.’”
Experts say reducing methane emissions from cattle is a key step toward achieving worldwide climate goals, because methane can trap 28 times more heat in the atmosphere than carbon dioxide does. Methane is also the second most abundant greenhouse gas emitted by human-related activities. Starting in 2030, cattle farmers in Denmark will have to pay taxes on methane emissions from their livestock, as the country implements what is believed to be the world’s first tax on agricultural emissions.
