Seaweed rewires cow guts to dramatically slash methane

A single dairy cow can burp roughly 200 pounds of methane into the air each year, adding a powerful heat-trapping gas to the atmosphere.

Now, researchers have identified a promising biological fix hiding inside the cow’s own gut.

A team led by Matthias Hess, a microbiologist at the University of California, Davis, found that red seaweed helps cow gut microbes produce far less methane.

In a controlled eight-cow study, animals that ate seaweed for 14 days released about 60 percent less methane while staying healthy and productive.

Cow burps matter for climate

Globally, livestock are responsible for roughly one-third of human-caused methane emissions, based on estimates from various governmental assessments.

That share matters because methane warms the planet quickly, especially during the first few decades after it is released. In cattle, most of this methane comes from the rumen, the main fermentation chamber in a cow’s stomach.

Inside this warm, low-oxygen space, specialized microbes turn hydrogen and carbon into methane and send it back up and out as burps.

Seaweed changes cow digestion

Red seaweed in the genus Asparagopsis makes compounds that block key enzymes in methane-forming microbes.

A broader review of seaweed research outlined how this alga produces bromoform and other molecules that interfere with methane-forming enzymes.

Earlier feeding trials showed that adding Asparagopsis to dairy cow diets could cut methane emissions by about two-thirds without hurting productivity.

One controlled experiment in lactating cows captured these large cuts under barn conditions.

Hess and his colleagues studied eight Holstein cows fed either a regular diet or the same diet plus a little dried red seaweed.

The seaweed-fed cows produced less methane and more hydrogen. They also turned their feed into milk more efficiently, with feed efficiency rising by three-quarters.

A new microbe emerges

To understand why, the team sequenced DNA and RNA from the microbes living in each cow’s rumen.

The genetic readouts showed which microbial genes became more active or less active when seaweed was in the mix.

When seaweed shut down the usual methane makers, hydrogen briefly built up in the rumen. Too much hydrogen can make the rumen more acidic and cause health problems if another group of microbes does not step in.

Microbe that flips the switch

The sequencing work pointed to a previously uncultured bacterium from the genus Duodenibacillus that seemed eager to soak up this extra hydrogen.

This microbe flourished in seaweed-fed cows and switched on genes that let it use hydrogen as an energy source.

“Instead, this organism uses the hydrogen and converts it to succinate, a compound the animal can eventually use to make protein,” said Hess.

Too much hydrogen in the rumen can damage the cow’s health if no other microbes pick it up.

Cow microbes battle for hydrogen

Microbes that make methane in ruminants rely on hydrogen as a main fuel and act as the dominant hydrogen sink in the rumen.

If another microbe grabs that hydrogen first, the methane formers are starved of fuel and the gas output falls.

“Hydrogen is a key energy source in the rumen, specifically for methane-producing microbes,” said Spencer Diamond, a principal investigator at the Innovative Genomics Institute.

Diamond noted that other native microbes can capture that hydrogen instead and help animals use it more efficiently.

Shutting down methane production might sound like it would slow digestion. Instead, the seaweed-fed cows showed higher feed efficiency. This suggests that less energy left their bodies as gas and more stayed in useful molecules.

Cow gas levels expose the change

Hydrogen levels in those animals rose sharply when methane fell, which fits the idea that methane formers act as a major outlet for this gas in the rumen.

The new hydrogen-hungry bacteria helped keep that buildup in check and funneled some of the energy toward compounds the cow can use.

Those shifts hint that the rumen microbiome, the complete collection of microbes in a cow’s stomach, can settle into a new, stable state with much lower methane.

That new balance keeps digestion humming while giving the atmosphere a break.

Microbes offer a new route

Seaweed supplements can be costly and hard to deploy on vast pasture systems. They also rely on large-scale seaweed farming, which raises its own environmental and supply questions.

The genetic blueprint of the seaweed-treated rumen now hints at a different path. If scientists can isolate Duodenibacillus and similar hydrogen-hungry microbes, they may someday build probiotic mixes that tilt the rumen toward these species without needing seaweed in every meal.

Because the new work mapped which genes switched on when methane dropped, it also offers targets for selective breeding.

Breeding cows for cleaner air

Cows that naturally favor these hydrogen-scavenging microbes or pathways might be bred so future herds belch less methane from birth.

As pressure grows to cut agricultural methane, tools that work from inside the animal will be valuable alongside policy changes and manure management.

This study shows how scientists can steer a cow’s gut community toward a lower-methane, more efficient state by reshaping who gets to eat the hydrogen.

The study is published in the journal Microbiome.

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