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Davis, California

Saturday, May 18, 2024

Seaweed may help reduce dairy cattle methane emissions

Seaweed is incorporated into the diet of cattle. (ALICE ROCHA / COURTESY)

First animal trials connect bovine seaweed consumption to lower enteric methane emissions

California’s Senate Bill 32 has called for a greenhouse gas (GHG) reduction in the state of California. By the year 2030, the state hopes to be 40 percent below 1990 level emissions. This calls all industries into action, including California’s massive and influential dairy industry. In order to meet the pressure of decreasing emissions, UC Davis researchers from the Department of Animal Science have started the world’s first seaweed animal trial. Based off several in vitro trials in Australia, two professors started feeding a dozen Holstein cows seaweed about a month and a half ago in hopes of replicating the potential the past studies have shown.

One of the investigators, animal science professor Ermias Kebreab, held a media event on May 24 to showcase the new and promising research.

8 percent of GHG emissions come from agriculture, Kebreab said. Several estimates from the Air Resources Board show that 60 percent of this is attributed to methane, 30 percent of which comes from enteric fermentation, 25 percent from manure and 3 percent from rice production along with some other sources.

The trial started with in vitro trials, performed by Matthias Hess, another professor in the Department of Animal Science.

“We used an artificial gut system to mimic a rumen,” Hess said. “This allows us to screen for the most efficiency dosages of seaweed and the best means of administering it. The artificial gut acts like a small bioreactor using a sample of rumen fluid from a fistulated cow. How a cow reacts to a treatment will vary because each animal has a unique microbiota within her gut. Because of this, we mixed the samples together to homogenize the microbes present.”

Some studies in the past have struggled to accurately measure the potential of seaweed as a methane suppressant, as they are unable to maintain the microbiota environments for prolonged periods. Hess’ artificial gut system allows the microbes to thrive in the controlled environment without dying off prematurely.

The in vitro trials performed on campus confirmed the potential of the seaweed, Asparagopsis armata, as an anti-methanogen. Although there are other species of seaweed like Asparagopsis taxiformis that have proven to be better methane suppressors, this seaweed does not grow as well in California as its A. armata counterpart.

The animal trials, taking place at the UC Davis Dairy, are composed of three different treatment groups receiving different amounts of the seaweed. The control group does not receive any seaweed and eats a normal total mixed ration like the other cows housed at the dairy.

The two treatment groups receive either 0.5 or 1 percent seaweed as a proportion of their daily intake, said Breanna Roques, the graduate student working on this trial. According to Roques, the dosage is determined by how much the cow normally eats. All the cows being used in this trial are Holsteins in the middle of their lactation cycles. In order to ensure that the cow eats the seaweed, it is finely ground by hand and mixed with molasses to improve its palatability.

Cattle are unique animals. With their rumens, they are able to ferment and digest just about anything they eat, especially things like brewer’s grains leftover from beer production, which humans cannot consume. However, in order to do so, they need to ferment indigestible substances like cellulose and lignin. All mammals, cattle included, have microbes living within their digestive systems. These microbes are responsible for producing the methane gas a cow breathes out. This is done to remove excess hydrogen from the rumen, which protects the microbes from an overly acidic environment.

The seaweed works to block the microbial enzymes responsible for generating methane gas, Hess said. It depresses the function of the microbes without depleting their natural population.

Using Green Feed, a turn-key system designed to measure gases like methane, carbon dioxide and hydrogen, Kebreab and Roques are able to determine how well the seaweed is reducing methane emissions.

A “cow cookie” drops into the Green Feed chamber, attracting the cow’s attention. It’s made up of all the things a cow loves, Kebreab said. As the cow eats and breathes with its head in the chamber, the gases are measured and sent to a lab in South Dakota.

Some people believe that most methane comes from a cattle’s flatulence. However, research has shown that only about 5 percent of methane is emitted from the rear end. The remaining 95 percent is released through a process called eructation, also known as burping.

Green Feed is only one of the means researchers can use to measure GHG emissions from cattle. Other forms are head chambers and sulphur hexafluoride tracers.

Many studies have gone into comparing the accuracy of these different systems, Roques said. But all the results show similar accuracy. In addition, the Green Feed system has better flexibility and mobility without having to limit where research can be done.

With the relative newness of the trial and its unique position, there are not many results available, but Kebreab said they have been seeing reductions of upwards of 30 percent in the cows’ emissions.

The work does not end there. The ultimate goal would be to make this method and the seaweed commercially available to all producers, but this remains several years worth of testing away. Further testing in the coming months will determine the safety and product quality of the milk coming from cows receiving seaweed in their diets. Due to the low dosages, it is not expected that the seaweed will cause a change in milk taste, but research is needed to confirm this.

“We are going to have a milk tasting panel, sampling 150 gallons of pasteurized milk from these cows,” Kebreab said. “We’re going to see if people can notice a difference between the cows eating seaweed and those that are not.”

The research team also plans on performing a similar, but much longer trial using beef steers at the UC Davis feedlot.

To make this work feasible and widespread, there needs to be more work put into the seaweed industry. Kebreab has been working with several marine biologists to make seaweed collection and feeding more cost-effective.

The main objective of this testing is to see if seaweed reduces methane emissions in an efficient manner without negatively impacting the cow’s health and body composition or decreasing milk yield. Early results have provided surprisingly positive outcomes with the future of seaweed research looking bright.



Written by: Alice Rocha — science@aggie.org



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