Feeding cows seaweed cuts methane emissions by almost 40%, study reveals

Feeding grazing beef cattle a seaweed supplement in pellet form reduced their methane emissions by almost 40% without affecting their health or weight, researchers have found in a new study into mitigating methane emissions from cattle.

The research, conducted by the University of California, Davis, is the first to test seaweed on grazing beef cattle, and academics hope it could be a valuable tool in fighting climate change. Its findings show that using seaweed reduced methane emissions by 82% in feedlot cattle and over 50% in dairy cows.  

“Beef cattle spend only about three months in feedlots and spend most of their lives grazing on pasture and producing methane,” says senior author Ermias Kebreab, professor in the Department of Animal Science.

“We need to make this seaweed additive or any feed additive more accessible to grazing cattle to make cattle farming more sustainable while meeting the global demand for meat.”

Livestock accounts for 14.5% of global greenhouse emissions, with the largest portion coming from the methane cattle release when burping. Grazing cattle also produce more methane than feedlot cattle or dairy cows because they eat more fiber from grass. The US has nine million dairy cows and over 64 million beef cattle. 

Fighting climate change

The US Environmental Protection Agency estimates that a single cow produces between 154 and 264 pounds of methane gas annually. 

According to Kebreab, the daily feeding of pasture-based cattle is more complex than feedlot or dairy cows because they often graze far from ranches for long periods. However, ranchers often supplement their diet during the winter or when grass is scarce. 

Beef steers graze on a ranch in Dillon, Montana, taking part in the research. (All image credits: Paulo de Méo Filho / UC Davis)

The study divided 24 beef steers — a mix of Angus and wagyu breeds — into two groups. One group received the seaweed supplement and the other did not. The ten-week experiment was conducted at a ranch in Dillion, Montana, in the US. Even though these were grazing cattle, they ate the supplement voluntarily, which still resulted in a nearly 40% cut in emissions. 

Most research studies on reducing methane emissions using feed additives have taken place in controlled environments with daily supplements. But Kebreab says that in the study, fewer than half of those methods are effective for grazing cattle. 

 “This method paves the way to make a seaweed supplement easily available to grazing animals,” he says. “Ranchers could even introduce the seaweed through a lick block for their cattle.” 

Pastoral farming often includes large grazing systems and supports millions of people worldwide, often in areas vulnerable to climate change. The university hopes the study offers a solution for more climate friendly cattle farming.