By Miranda Lipton
New research from the University of California, Davis on feeding seaweed to grazing cattle shows that the practice could significantly reduce the greenhouse gases released by livestock, which produce roughly 14.5 percent of the climate-warming emissions.
The peer-reviewed study, published in December 2024 by the Proceedings of the National Academy of Sciences, was led by three researchers in the Department of Animal Science. It found that incorporating seaweed into the diets of grazing cattle, which outnumber any other type of cattle by a factor of three, can reduce methane emissions by nearly 40 percent. Now, there are two major stepping stones to integrating this treatment at a commercial scale: gaining FDA approval, and making it palatable enough for cows to eat willingly.
The study focused specifically on Asparagopsis taxiformis, a red seaweed species that is being scaled for methane reduction. While earlier research had examined seaweed’s effect on cattle digestion, this was the first study to focus specifically on how to feed it to cattle grazing on wild grasses in open pastures and on sprawling public lands, which poses logistical challenges compared to confined livestock.
“All of the studies except this one have been done in a confined situation,” said Ermias Kebreab, a researcher on the UC Davis study. “And it’s pretty easy to add additives when you’re in control of their diets…but most animals are grazing.”
As Kebreab explained, grazing animals are a far bigger piece of the puzzle than their feedlot counterparts—and not just due to the number of them. Grazing cattle produce more enteric methane per head than feedlot cattle or dairy cows due to the high-fiber content of their grass-based diet.
In the winter, when the grass in pastures isn’t growing as quickly and is often covered by snow, especially in northern climates, cattle diets are supplemented in barns. That’s where the UC Davis team introduced seaweed into the feed and began to monitor its impact.
“We used a combination of techniques, including breath analysis and monitoring methane concentration in exhaled air, to measure the impact of seaweed supplementation,” said Kebreab.
In the summer months, when the cows no longer need to be centralized to supplement the nutrients in their diets, researchers incorporated the seaweed into mineral-rich lick blocks to continue testing its efficacy in more natural grazing conditions.
Juliana Ranches, assistant professor at Oregon State University’s Agricultural Research Center, is on a team working to develop free-choice supplements that can be placed in pastures and don’t require routine distribution to reach grazing cattle.
“Producers will at times supplement grazing cows, but only in extreme circumstances,” said Ranches. “It’s labor intensive, so ideally we want to develop something where labor isn’t involved—something that they put in the pasture and go check on once every week or two.”
But there needs to be consistent intake for the supplements to work, so the taste of the seaweed is important to ensure the cattle will voluntarily choose to eat it.
“This [UC Davis] study showed us that this works really well with grazing cattle, but we still need to refine the palatability of the seaweed,” said Kebreab. “If we can work that out, we should be able to achieve significant reductions in methane.”
The studies are in their early stages, so more long-term research on how seaweed impacts the health of cattle, and how it affects their milk and meat, before the FDA will approve the supplements for commercial use.
One dairy farm that’s ahead of the curve, Straus Family Creamery in Northern California, has been experimenting with red seaweed for years as part of its broader goal to achieve carbon neutrality.
Joseph Button, Straus’s sustainability director, shared the results of a 60-day trial conducted under the auspices of the California Department of Food and Agriculture and the National Organic Program. “Our trial showed methane reductions of up to 90 percent, which aligns with the promising findings from UC Davis,” said Button. “This research gives us the scientific backing to continue pursuing seaweed supplementation as a key part of our emissions-reduction strategy.
Regulatory approval of seaweed in cattle feed has been slowed by the debate over whether they should be classified as a food supplement or a drug. “The reason that this is not already being used in California today, is because certain regulators determined that it probably needed to be considered a drug because it is so effective,” said Button.
However, since seaweed is a natural, unmodified substance, the approval process might be quicker than with drugs made from synthetic chemicals.
“Once the FDA approves this for full-scale use, we believe it will be instrumental in achieving carbon neutrality on our farm,” said Button. “This is crucial, as methane emissions from cows account for about 40 percent of on-farm emissions.”
The team at UC Davis noted that research on the emissions associated with the production and distribution of the supplement is needed to determine the full climate footprint of the supplement.
But, while not immediately on the horizon, there is a possibility that farmers could be taxed on the methane their cattle produce, as was recently proposed in Washington state, making emissions reduction strategies even more critical.
Cost remains a concern for many producers, but once seaweed is approved for use on a broader scale, its cost will decrease. “Like any new product, it’s expensive when it first hits the market, but once production ramps up, prices will drop,” Button said.
The seaweed might not need to be given throughout the duration of the cattle’s life. UC Davis is now in the midst of trials testing the effect of feeding seaweed to cows in just the early stages of a cow’s life, to see whether that can make permanent changes to the digestive tract.
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