Cattle were first domesticated from wild aurochs about 10,000 years ago, as a portable source of wealth for our ancestors, and have proliferated alongside us ever since. There are now about 1.5 billion cattle on Earth, making a lot of milk and meat for human consumption, but in the process, creating a tremendous amount of waste.

Not only do cows pollute groundwater with their excrement, they also produce a lot of gas. Headlines are fond of discussing the issue of cow farts, but in reality, the gas that scientists are concerned about—methane—comes mostly from cow burps. Methane is a potent greenhouse gas, with a climate change impact 25 times greater than carbon dioxide.

Earlier this year, researchers from Denmark's Aarhus University launched a four-year study to gauge whether adding a potent type of Greek oregano to cow feed could reduce methane emissions from dairy cow belches. Earlier research led by Penn State scientists suggested that oregano could cut cows’ methane emissions up to 40 percent.

Now, Australian researchers have found even more promising results from a beach staple (or nuisance, depending on your perspective): seaweed. Scientists on the Agriculture and Food team at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) showed introducing a particular kind of seaweed, Asparagopsis taxiformis, to livestock feed can reduce the methane production in sheep by more than 80 percent. Some of those researchers also did experiments with artificial cow stomachs, which found even higher potential reductions.

“Seaweed’s been fed to cattle since farming began,” agricultural scientist Robert Kinley, part of the CSIRO team, told mental_floss. Anywhere it washed up on beaches near where cows grazed, the animals would eat it, so it’s long been a natural food source. But after a farmer on Prince Edward Island in Canada noticed in 2006 that his cows that ate seaweed were healthier than those that he kept inland, researchers—including Kinley, then at Nova Scotia's Dalhousie University—began investigating. 

“Nobody really cared about seaweed until 10 years ago, but since then there have been various seaweeds on the market because it improves animals’ reproductive success and makes for healthier, happier animals,” says Kinley. Cows that eat seaweed have more efficient digestion, with 10 to 20 percent fewer methane emissions. Methane only persists in the atmosphere for about 10 years, as opposed to carbon dioxide’s hundreds of years, so cutting how much methane cows produce could help immediately address climate change impacts.

For farmers, better cow digestion creates economic benefits by making the cost of feed more efficient. So supplementing feed with seaweed has recently become a trend, and that’s where Kinley got involved—he wanted to make sure seaweeds were safe for cows to eat regularly. As he was testing different types of seaweeds, he wondered if there was one that might cut methane even more than 20 percent. He reached out to a group at CSIRO "who already had some ideas about the unique chemistry of seaweeds," he says. They began collaborating. "We wanted to find seaweeds that would benefit animals and reduce greenhouse gas emissions too."

They found what they were looking for in Asparagopsis taxiformis, a red seaweed. It aids digestion as other seaweeds do, but has an additional gas-reducing function. “The big punch comes from an enzyme inhibition. The seaweed chemistry debilitates the methanogen process so the pathway to form methane can’t be completed,” says Kinley. This leads to cows producing much less methane—a reduction of 99 percent in preliminary tests on the artificial cow stomachs. However, that reduction was dependent on a constant supplementation of the seaweed to keep the methane-reducing benefits going. Once the supplementation was stopped, methane production went right back up.

Kinley and his colleagues are now working on health protocols to establish the seaweed is safe for long-term consumption; next up is a feedlot trial with cows to determine what minimum amount of seaweed supplementation is needed for methane reduction.

Kinley sees an opportunity to create jobs by cultivating seaweed farming in places where A. taxiformis grows, which is pretty much everywhere; it's a cosmopolitan species with multiple lineages (and is considered invasive in some locations). Right now, no one’s farming it, which presents a barrier to scaling up. “The biggest barrier isn’t animals or time, it’s how much seaweed can we get?” says Kinley. “Right now, I need 25 tons of seaweed just to do a feedlot trial with 1000 animals.”

But if cultivation takes off, the seaweed could be a quadruple win—helping clean wastewater and remove runoff nutrients and carbon dioxide near reefs, growing happy cows, aiding farmers, and mitigating climate change.