Dairy cows’ methane emissions were cut in half by a new feed additive in a commercial trial on the Straus Dairy, signifying an important step toward the farm’s goal of becoming carbon neutral by 2023. The trial showed that the additive, red seaweed, can work as well on a real dairy as it has in the lab. But the seaweed could be challenging to produce on a large scale.

“To have a product that was able to perform like this on a farm is pretty astonishing and really exciting,” said Randi Black, a dairy advisor at University of California Cooperative Extension. But, she added, “right now, it is not an economically feasible feed additive, simply because it hasn’t been scaled.”

Over the summer, two dozen cows on the Marshall farm were fed a few ounces of powdered asparagopsis, an edible red algae, along with their hay and alfalfa. Another 24 cows ate their regular feed as a control group. The methane emissions in the cows’ burps were measured using a device called a GreenFeed. The cows that ate the seaweed showed a 52 percent average reduction in enteric methane over 50 days. A few cows had reductions of up to 90 percent. 

The trial was sponsored in part by Blue Ocean Barns, a company that is experimenting with growing red seaweed for use as feed. A 2019 study from the University of California, Davis showed reductions of up to 67 percent when cows on a research dairy were fed red seaweed. The Straus trial was the first on a commercial dairy. 

Scientists are experimenting with other feed additives aimed at reducing methane emissions, though none are on the market yet. A chemical additive known as 3NOP has also been promising but, as a synthetic feed, it can’t be used for certified organic operations. Red seaweed appears to be the best bet for Marin’s organic dairy farms in the future. 

It could take years for the use of red seaweed to become widespread, however. The Straus trial used seaweed leftover from the Davis trial that was harvested in the Azores, but Blue Ocean Barns has begun growing the seaweed on land in commercial tanks in Hawaii and San Diego. 

Albert Straus, owner of Straus Dairy Farm and Straus Family Creamery, had to secure a special allowance from the United States Department of Agriculture’s National Organic Program to use the seaweed, and the product will need regulatory approval to be used elsewhere. 

Cost is a major concern because of the small scale of seaweed production. Dairy farmers already spend 50 to 70 percent of the cost of their milk on feed, Ms. Black said, so if feed costs increase, it could put farmers out of business. 

“Economies of scale are going to hopefully make seaweed affordable,” Ms. Black said, “but in the end it’s going to need to be pennies to the gram.”

Mr. Straus was hopeful that the relatively small quantities necessary—just one to three ounces per 45 pounds of feed—wouldn’t break the bank for farmers. 

But there are other questions. A 2019 study by Penn State University researchers raised some doubts about the large-scale and long-term efficacy of red seaweed. Cows’ rumens tend to adapt to new feeds, which could weaken the methane-reducing effects of the seaweed over time. The active ingredients in the seaweed are also sensitive to heat and sunlight, the researchers wrote, raising questions about the additive’s shelf life. 

State law mandates a 40 percent reduction in methane emissions by the end of the decade, and Straus Family Creamery has been active in developing and promoting new methods for doing so. The farm’s methane digester, rotational grazing procedures, and fully electric trucks are already in effect. 

In 2020, the creamery’s operational greenhouse gas emissions increased by 8 percent, which it attributed to temporarily operating two creameries at once as it moved its production plant from Marshall to Rohnert Park. The energy usage for construction and transportation at the new Sonoma County facility explained the jump from about 1,600 to more than 1,700 metric tons of carbon dioxide equivalent since 2019. 

And the company’s operational emissions numbers don’t include the methane emissions of individual dairy farms that supply it. Last year, Mr. Straus’s own dairy measured about 1,863 metric tons of CO2 equivalent. 

Mr. Straus said he hopes to expand the use of red seaweed to all his company’s 12 suppliers, but the seaweed will first need organic certification and regulatory approval. 

Two of his suppliers are in the Point Reyes National Seashore: the Drakes View Dairy at A Ranch and the Mendoza Dairy at B Ranch. In the seashore’s newly amended management plan, the National Park Service committed to identifying and pursuing strategies to reduce greenhouse gases on its ranches to meet state and federal emissions goals. The plan specifically cites “new feed types that reduce methane from cattle” among the innovations to consider. 

“I’ve met with the park about how we can collaborate and show a model for sustainable farming in the seashore,” Mr. Straus said. 

Opponents of ranching in the park have pointed to methane emissions as a central concern, and Mr. Straus said he hopes his emissions goal will address that. “We can help improve the public view of dairy farms,” he said. “Painting the dairy farms in the park as a Central Valley confinement area is inaccurate. We can show that organic dairy farms are actually beneficial.” 

This article was corrected and clarified since its original publication date.