Beef steers graze on a ranch in Dillon, Montana. The machine nearby releases a seaweed supplement while also measuring the cattle’s methane emissions. Credit: Paulo de Méo Filho/ UC Davis.

Feeding grazing cattle on seaweed cuts methane emissions by almost 40%, opening up a route to more climate-friendly farming.

Seaweed is once again showing promise for making cattle farming more sustainable.

A new study by researchers at the University of California, Davis, found that feeding grazing beef cattle a seaweed supplement in pellet form reduced their methane emissions by almost 40% without affecting their health or weight.

This is the first study to test seaweed on grazing beef cattle in the world.

It follows previous studies that showed seaweed cut methane emissions 82% in feedlot cattle and over 50% in dairy cows.

How much methane do cattle produce?

Livestock account for 14.5% of global greenhouse gas emissions, with the largest portion coming from methane that cattle release when they burp.

Grazing cattle also produce more methane than feedlot cattle or dairy cows because they eat more fibre from grass. In the US, there are nine million dairy cows and over 64 million beef cattle.

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

“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.”

Difficulty in lowering emissions

Kebreab said that daily feeding of pasture-based cattle is more difficult than feedlot or dairy cows because they often graze far from ranches for long periods.

However, during the winter or when grass is scarce, ranchers often supplement their diet.

For this study, researchers divided 24 beef steers (a mix of Angus and Wagyu breeds) into two groups: one received the seaweed supplement, and the other did not.

Researchers conducted the ten-week experiment at a ranch in Dillon, Montana.

Since these were grazing cattle, they ate the supplement voluntarily, which still resulted in a nearly 40% cut in emissions.

Most research to reduce methane emissions using feed additives have taken place in controlled environments with daily supplements, but Kebreab noted in the study that fewer than half of those methods are effective for grazing cattle.

He said: “This method paves the way to make a seaweed supplement easily available to grazing animals.

“Ranchers could even introduce the seaweed through a lick block for their cattle.” 

Kebreab said pastoral farming, which includes large grazing systems, supports millions of people around the world, often in areas vulnerable to climate change.

This study suggests a way to make cattle grazing better for the environment and play a role in fighting climate change. 

The study is published in Proceedings of the National Academy of Sciences.