Emissions from the world’s nearly 1.5 billion cattle are a major source of methane, a powerful greenhouse gas. Now, researchers in California and elsewhere are experimenting with seaweed as a dietary additive for cows that can dramatically cut their methane production.

The spring morning temperature in landlocked northern California warns of an incipient scorcher, but the small herd of piebald dairy cows that live here are too curious to care. Upon the approach of an unfamiliar human, they canter out of their barn into the already punishing sun, nosing each other aside to angle their heads over the fence. Some are black-and-white, others brown; all sport a pair of numbered yellow ear tags. Some are more assertive than others. One manages to stretch her long neck out far enough to lick the entire length of my forearm. “That’s Ginger,” explains their keeper, 27-year-old Breanna Roque. A graduate student in animal science at the University of California, Davis, Roque monitors everything from the animals’ food rations to the somatic cells in their milk — indicators of inflammation or stress. “The interns named her. She’s our superstar.” Ginger is one of 12 Holstein cows participating in an experiment being conducted by Roque’s animal science professor, Ermias Kebreab, into reducing methane emissions from livestock by supplementing their diets with a specific type of seaweed. Methane is a potent greenhouse gas, with roughly 30 times more short-term, heat-trapping power than carbon dioxide. In California alone, 1.8 million dairy cows, together with a smaller number of beef cattle, emit 11.5 million metric tons of carbon dioxide equivalent every year — as much as 2.5 million cars.

In the U.S., domestic livestock contribute 36 percent of the methane humans cause to be put into the atmosphere.

The enormity of those numbers, in part, motivated California lawmakers to pass a law to reduce methane emissions and other short-lived “climate pollutants” by 40 percent below 2013 levels by 2030. The California Air Resources Board subsequently ordered a majority of the reductions in the new law to come from the dairy industry. Other cuts will come from diverting organic waste from landfills and eliminating fugitive emissions associated with oil and gas operations. The UC Davis study will contribute to a global store of knowledge on how to limit the methane produced by “enteric fermentation” — the digestive process in a ruminant’s upper stomach chamber, or rumen, where microbes predigest fiber and starch, releasing gases when they belch and exhale. It’s “one of a handful of options in various stages of development that seem to have the potential to reduce [enteric] methane by 30 percent or more,” says Ryan McCarthy, science advisor to the Air Resources Board. Kebreab’s experiments with seaweed additives to cattle feed have now surpassed that 30-percent figure, with one type of seaweed slashing enteric methane by more than 50 percent. In the fight to slow climate change, such reductions are no small matter: In the United States alone, domestic livestock — including cattle, sheep, goats, and buffalo — contribute 36 percent of the methane humans cause to be put into the atmosphere, according to the U.S. Environmental Protection Agency.

Scientist Ermias Kebreab has studied how to reduce cow methane emissions for more than a decade. Gregory Urquiaga/UC Davis

Researchers worldwide are working on the livestock methane problem. In the past, scientists have tried mixing microbes from the low-methane-producing kangaroo forestomach into bovine gut microbes, selectively breeding less gassy cows. Researchers have also tried vaccinating to suppress “methanogens” — the bacteria that turn carbon and hydrogen into methane in the rumen. (That last idea was a little like trying to develop a flu vaccine that would work every year, in every corner of the world. “There were too many different methanogens,” Kebreab says. “We couldn’t calibrate it for all of them.” ) Feed additives have shown more promise. Three years ago, Alexander Hristov, a researcher at Penn State University, achieved a 30 percent reduction in enteric methane by salting ruminant feed with a substance called 3-nitrooxypropanol, or 3NOP (the substance is currently awaiting FDA approval). Kebreab believes seaweed might prove to be an even better solution. A native of Eritrea who came to the U.S. after working in the United Kingdom and Canada, the 45-year-old researcher has been working on the problem for 15 years. “It’s taken up pretty much my whole career,” he says. In the research barn at UC Davis, Roque opens a large foil bag to reveal fistfuls of dried algae the color of old bricks: Asparagopsis, still off-gassing the ocean — fish and sulfur with bright notes of iodine. Interns have ground up the clumps and poured them into orange buckets. Roque puts on latex gloves to blend the dried seaweed with molasses to produce a shiny, viscous slop that the cows evidently find delicious. Palatability is key: One study in the UK that added curry to feed in a simulated cow rumen looked promising until the real-life cows refused to eat the curry. “They’re pretty picky eaters,” Roque says. Foraging animals have to sort nourishment from potential poisons in the pasture. “If they run across something unfamiliar, they’ll avoid it.”

Farmers in ancient Greece and 18th-century Iceland deliberately grazed their cows on beaches.

Four of the cows eat a mixture of alfalfa and hay, heavily spiked with the seaweed-molasses mixture. Four more will eat the same feed, with less seaweed added in. The rest are the control group — they’ll eat plain feed, without any additives at all. Roque spent nearly two weeks training the cows in how to access their own specific feeding berths, affixing each one with a transponder that allows the cow to open an electronic door to her individual trough. Not all the cows are down with the program. One, large, black-masked Holstein repeatedly shoves her smaller, more compliant neighbor aside from the open door of her berth. The smaller cow obliges every time. Roque raps the bolder cow on the nose, and it withdraws, but not for long. “They’re eating the exact same thing,” Roque says, a bit exasperated. In the paddock as in the pasture, “the grass really is always greener.” When they finish eating, they’re enticed by the drop of a “cow cookie” to visit a compartment where an instrument, much like a breathalyzer, analyzes their emissions. “They hear it drop and come over,” Roque says. “We try to get each of them there three times a day.” Each cow wears a ring on its ear that transmits an identification code along with its breath analysis to a database. Roque and Kebreab can view the results on their computers and smartphones. WATCH: A look at how scientists are measuring methane from cows. (Credit: UC Davis)

The results have exceeded everyone’s expectations, including Kebreab’s. His three-month study of Ginger and her cohort found that spiking cows’ ordinary rations with one kind of marine macroalgae in particular, Asparagopsis, reduces enteric methane by 58 percent. More than other seaweeds, Asparagopsis contains compounds that inhibit the production of methane, or CH 4, and interrupt the process by which carbon and hydrogen bind together. “We did not expect these numbers in the doses we used,” Kebreab says. Milk production held steady or increased. A panel of tasters detected no differences among the different cows’ milk. There’s nothing novel about cows eating seaweed, notes Joan Salwen, an environmental science fellow at Stanford University who introduced UC Davis scientists to the seaweed solution, and formed a nonprofit, Elm Innovations, to help focus and fund research. “Cows eat what’s available,” she says. In California, they eat almond hulls; in Georgia, they eat cottonseeds. Documented evidence attests to farmers in ancient Greece and 18th-century Iceland deliberately grazing their cows on beaches. It was, in fact, an ordinary farmer who hit upon the idea of supplementing cows’ feed with seaweed — not for the climate, but simply for his animals’ overall health. On the shores of Prince Edward Island in Canada, Joe Dorgan observed that his beach-paddocked cows got pregnant faster and produced more milk than his inland pastured cows. When he retired from dairy farming in 2011, he launched a new business, North Atlantic Organics, to make “stormtoss shoreweed” from Prince Edward Island available to inland farmers who graze their cows during seasons of scanty forage.

Because it appears to promote milk production, the seaweed cure might catch on in other dairy states.

When Dorgan wanted data to market his product, he approached an environmental scientist named Rob Kinley, who was then at Dalhousie University in Nova Scotia. In 2014, Kinley and his colleague Alan Fredeen analyzed different varieties of seaweed that washed up on beaches, mixed in vitro with rumen microbiota, for their nutritional value and health impacts on ruminants. But being environmental scientists, Kinley says, “‘what if?’ possibilities are always in our peripheral vision.” With an interest in how all livestock feeds affect enteric methane, they measured their samples for methane production as well. Kinley discovered in his laboratory tests that seaweeds could reduce methane production by as much as 16 percent. “That was the spark to deepen the search for more potent seaweeds,” he says.

By this time, Kinley had moved to Australia, where he went to work at the Commonwealth Scientific and Industrial Research Organisation (CSIRO). In partnership with James Cook University and Meat and Livestock Australia, Kinley began screening different seaweeds for their impact on methane emissions from ruminant livestock. That process revealed Asparagopsis as the anti-methanogenic seaweed of choice. But Kinley is quick to warn that it does not grow in abundance all over the planet. If it breaks out as a global solution to enteric methane, it will need to be farmed. Which is not, Kinley argues, a bad thing. Seaweed cultivation takes up excess nitrogen and dissolved carbon dioxide from ocean waters; cultivating it could create new economies in impoverished regions. Researchers still need to figure out how that would work. “There is no depth of knowledge in cultivation of Asparagopsis using any method,” says Kinley.

Ground-up Asparagopsis, a type of seaweed, which can reduce cow methane emissions up to 50 percent when added to feed. Gregory Urquiaga/UC Davis

“As far as we know,” says Salwen, “this supplement, if it proves out in all animal testing, could be offered in all livestock production systems that we know about.” Pasture-raised cows that eat primarily grass could have the supplement added to their water or to their salt licks. Even though the California dairy industry at large fought hard against what farmers initially considered onerous regulation, at least some dairy farmers are tentatively enthusiastic about seaweed additives. “Methane is an indication of an inefficiency in the animal’s digestion,” says Jonathan Reinbold, sustainability program manager for Organic Valley, a cooperative of more than 1,800 dairy farmers, including 35 in California. “If you can increase the digestion efficiency of a cow by 5 percent you could remove 5 percent of the land you use for production for cows. It can go back to fallow or be used to grow other kinds of food.”