by Elana Manasse-Piha
While the volume of methane emissions is only 1/200 that of carbon dioxide, according to the Intergovernmental Panel on Climate Change (IPCC), it will be 86 times more potent than carbon dioxide at warming the atmosphere over the next 20 years.
Worldwide, livestock is responsible for 14.5% of human-induced methane emissions. In the U.S., about 37% of human-induced methane emissions come from the agricultural sector. Within those emissions, the two largest sources of methane are enteric fermentation (basically animal burps) and manure management. In short, cattle are by far the largest contributors to agricultural methane emissions.
Currently, there are about 1.5 billion cattle worldwide, and the number is rapidly growing as demand increases for beef and dairy products. With every cow producing 154 to 265 lb methane/year, the combined impact cattle have on climate change is greater than the total impact of China.
To remedy the issue, we first need to understand its cause. When cows eat, the food goes into a special stomach called a rumen. In the rumen, plant-based sugars are broken down by bacterial digestion and fermentation into smaller pieces including hydrogen and carbon dioxide. Small organisms (aka microbes) living in the rumen, called methanogens, use the hydrogen to produce nutrients for the cow — as well as by-products like methane. While a small amount, 5-10%, of this methane exits through the cow’s rear as gas and in manure, 90-95% exits through the cow’s esophagus as a belch. This process is called “enteric fermentation.”
Graphic illustrating enteric fermentation. Image: “Methane emission factors and carbon fluxes from enteric fermentation in cattle of Nepal Himalaya” (2020). Science of The Total Environment, Elsevier.
The best way to reduce the amount of methane produced by cows would be to stop breeding so many cows. But an assortment of dietary, lifestyle, economic, and political reasons currently prevent a full-stop in cattle farming from being a viable option. Given that cattle numbers are only likely to increase, scientists have been researching ways to decrease and/or capture the methane produced by cows. One of the more promising methods for achieving this is supplementing their diet with seaweed.
Studies have shown that adding a relatively small amount of seaweed to a cow’s diet can result in up to a 90% reduction in their methane production! Bromoform (CHBr3), found in seaweed, disrupts the methanogens in the cow’s rumen, reducing methane production.
The most promising type of seaweed is called Asparagopsis. Many species of seaweed contain bromoform. However, Asparagopsis has more highly concentrated bromoform than is typical and, uniquely, stores it in gland cells.
Photo of Asparagopsis taxiformis (Red Seaweed) taken at a depth of 40m at Ras il-Ħobż on Gozo’s south coast. Image: by Brian Azzopardi, Atlantis Diving.
There are some legitimate fears concerning bromoform, as it is a known carcinogen. While one study concludes bromoform can end up in cow’s milk, another concludes that it does not. These conflicting results may be due to small sample sizes, testing thresholds, and/or the amount of seaweed fed to the cows. Other studies have shown that when cows are fed Asparagopsis, bromoform is not detected in the meat, fat, organs, or even the feces of the animals. The best available scientific information on absorption strongly suggests that humans could, at most, be exposed to levels below normal daily exposure to bromoform through tap water.
Another potential issue is that bromoform depletes the ozone layer. However, because Asparagopsis stores its bromoform in gland cells, handling techniques (which are unfortunately obscured by trade secrets) ensure that the bromoform is not released until ingested by a cow.
Currently, there is nowhere near enough Asparagopsis to give to every cow in the world. While Asparagopsis isn’t commercially farmed yet, many other seaweeds are. Multiple companies are developing new and/or modifying current technology to grow the two species of Asparagopsis (armata and taxiformis) in the ocean and tanks on land. Companies and organizations including CH4 Global, Australia’s Sea Forest, and Greener Grazing have invested millions in facilities around the world.
Asparagopsis taxiformis harvested in the Azores. Image: Hristov Research Group/Penn State.
Besides reducing methane emissions in cattle, farming Asparagopsis has other benefits. It causes a decrease in local ocean acidification and improves the habitat for local marine species. Another potential benefit is increased productivity in cattle fed seaweed. While some studies saw no change in productivity, one showed that dairy cows fed seaweed produce more milk; another found that beef cattle fed seaweed converted food to body mass 20% more efficiently than cattle on a typical diet, meaning they needed less food. If these studies are accurate, feeding cows seaweed would be environmentally and economically beneficial.
What do you think? Is feeding Asparagopsis to cattle a good solution to lower their methane production, or should we push for breeding fewer cows? Let us know in the comments!
Banner image by Jan Koetsier from Pexels