Methane is a short-lived but powerful greenhouse gas and the second-largest cause of climate change after carbon dioxide. And most of the human-caused methane emissions come from livestock.
About 70% of agricultural methane comes from enteric fermentation – chemical reactions in the stomachs of cows and other grazing animals when they break down plants. The animals expel most of this methane and pass the rest on as flatulence.
There are about 1 billion cattle around the world, so reducing enteric methane is an effective way to reduce overall methane emissions. But most options for doing this, such as changing cows’ diets to more digestible feed or adding more fat, are not cost effective. A 2015 study suggested that using seaweed in addition to livestock’s normal feed might reduce methane production, but this study was done in a lab, not live animals.
We study sustainable agriculture, with an emphasis on livestock. In a newly published study, we show that the use of red seaweed (Asparagopsis) as a dietary supplement can reduce both methane emissions and feed costs without affecting meat quality. If these findings can be scaled up and commercialized, they can turn livestock farming into a more economically and environmentally sustainable industry.
Plant fermentation machines
Ruminants, such as cows, sheep and goats, can digest plant material that is indigestible by humans and animals with simple stomachs, such as pigs and chickens. This unique ability stems from the four-compartment stomachs of ruminants – specifically the rumen compartment, which contains a wide variety of microbes that ferment feed and break it down into nutrients.
This process also generates by-products that the cow’s body does not absorb, such as carbon dioxide and hydrogen. Methane-producing microbes called methanogens use these compounds to form methane, which is expelled from the cow’s body.
We first analyzed this problem in a 2019 study, which was the first study conducted in cattle rather than in a lab. In that work, we showed that supplementing dairy cows’ feed with about 10 ounces of seaweed per day reduced methane emissions by as much as 67%. However, the livestock that ate this relatively large amount of seaweed consumed less feed. This reduced their milk production – a clear drawback for dairy farmers.
Our new study sought to answer a number of questions that would be important to farmers considering using seaweed supplements on their livestock. We wanted to know if the seaweed was stable in storage for up to three years; whether microbes that produce methane in the stomach of cows could adapt to the seaweed, rendering it ineffective; and whether the type of diet the cows ate changed the seaweed’s effectiveness in reducing methane emissions. And we used less seaweed than in our 2019 study.
Better growth with less feed
For the study, we added 1.5 to 3 ounces of seaweed per animal to the feed of 21 beef cows daily for 21 weeks. As with most new ingredients in animal feed, it took the animals a while to get used to the taste of seaweed, but they got used to it within a few weeks.
As we expected, the oxen released much more hydrogen – up to 750% more, mainly from their mouths – because their systems produced less methane. Hydrogen has a minimal impact on the environment. Seaweed supplements did not affect the animals’ carbon dioxide emissions.
We also found that seaweed stored in a freezer for three years retained its effectiveness, and that microbes in the cows’ digestive system did not adapt to the seaweed in a way that neutralized its effects.
During the experiment, we fed each of the animals three different diets. This ration contained different amounts of dried grasses, such as alfalfa and wheat hay, also known as fodder. Cattle can also consume fresh grass, grains, molasses, and by-products such as almond husks and cottonseed.
Rumen methane production increases as the feed in the cow’s feed increases, so we wanted to see if the feed level also affected how well seaweed reduced overall methane formation. Methane emissions from cattle on high-food diets decreased by 33% to 52%, depending on how much seaweed they consumed. The emissions of cattle that were fed poverty decreased by 70% to 80%. This difference may reflect lower levels of an enzyme involved in the production of methane in the intestines of low-fiber bovine diets.
An important finding was that the oxen in our study convert feed up to 20% more efficiently into body weight than cattle on a conventional feed. This benefit could lower production costs for farmers as they would have to buy less feed. For example, we calculate that a producer who slaughters 1,000 beef cattle – that is, feeding them an energy-rich diet to grow and add muscle – could cut feed costs by $ 40,320 to $ 87,320, depending on how much seaweed the cattle consumed.
We’re not sure why feeding bovine seaweed supplements helped them convert more of their diet into weight gain. However, previous research has suggested that some rumen microorganisms can use hydrogen no longer used for methane production to generate energy-rich nutrients that the cow can then use for additional growth.
When a panel of consumers tasted meat from cattle raised in our study, they found no difference in tenderness, juiciness, or flavor between meat from cattle that ate seaweed and others that did not.
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Commercializing seaweed as a feed additive would involve many steps. First, scientists should develop aquaculture techniques to produce seaweed on a large scale, either in the ocean or in tanks on land. And the U.S. Food and Drug Administration should approve the use of seaweed as a dietary supplement for commercial livestock.
Farmers and ranchers could also earn money to reduce their livestock emissions. Climate scientists should provide guidance on quantifying, monitoring and verifying methane emission reductions from livestock. Such rules could allow livestock farmers to earn credits from carbon offset programs around the world.
This article was republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. It is written by: Ermias Kebreab, University of California, Davis and Breanna Roque, University of California, Davis
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Ermias Kebreab receives funding from the Foundation for Agricultural Research, Elm Innovations, the David and Lucile Packard Foundation and the Grantham Foundation. He advises feed additive companies such as Blue Ocean Barns and Mootral.
Breanna Roque does not work for, consult, own stock or receive funding from any company or organization that would benefit from this article, and has not disclosed any relevant affiliations outside of their academic appointment.