Hold off — for now — on feeding seaweed to cows to reduce methane

Since the United Nations COP26 climate summit, the race to reduce methane emissions from cattle production and to slow climate change appears to have officially started. Unofficially, animal scientists have been exploring the effects of feed additives to reduce methane production from beef and dairy cows for more than a decade; albeit, funding has been limited to adequately support such endeavors.

As attention on this challenge grows, one potential feed additive for cattle has found the limelight: seaweed. Feeding cows seaweed is a promising approach to “help slow methane emissions — and change the world.” We certainly should be optimistic — and the feeding strategy might be a critical breakthrough. But expectations should be tempered until its merit is evaluated by science.

The attention has focused on seaweed because it contains trihalomethanes, such as bromoform, which is an active ingredient that decreases methane emissions from cattle belches. But the reality is that there are thousands of species of seaweed. Red seaweed (e.g., Asparagopsis taxiformis) has been praised for inhibiting methane production from cattle by more than 80 percent because of its high bromoform content. In contrast, brown seaweed (e.g., Ascophyllum nodosum) has a lower bromoform content and is less effective at being antimethanogenic.

Widespread use of seaweed varieties will require large-scale cultivation for the cattle feed industry. Seaweed farming in oceans is possible but does have some environmental concerns. 

Different species of seaweed prefer cold or warm water at various depths. For instance, Asparagopsis taxiformis won’t grow off the coast of Maine because it prefers tropical or sub-tropical climates. We also have to examine how seaweed farming would impact marine mammal diversity and potentially contribute to ocean pollution. Bromoform from seaweed may also have an ozone-depleting effect, but its impact is not fully understood. Land-based aquaculture systems in controlled environmental conditions or the production of bioactive ingredients using bioengineering are underdeveloped investment opportunities that might meet the demand for seaweed and be more environmentally friendly.

Processing and distribution of seaweed is another challenge.

Raw seaweed is wet and heavy. This creates a transport issue from the harvest site to the processing facility. Seaweed will need to be dried and ground. The final product will need additional transport to the feed mill or farm, which could be significant to feed cattle in the Midwest. Shelf-life of the raw and final product, and waste, will also need to be investigated. These are all factors that may increase fossil fuel consumption and affiliated greenhouse gas emissions. A life cycle assessment is needed to ensure that we don’t increase methane and carbon dioxide emissions more than by not feeding cows seaweed at all.

We also need to learn more about how feeding seaweed impacts cow biology.

We want to feed cattle additives that enhance meat and milk production and quality, and promote animal health with less feed, nutrient waste, and cost. But we know so little about whether the ability of seaweed to inhibit methane production is influenced by changes in the animal’s diet, digestion, microbiome, or genetics. Does seaweed impact feed intake, growth, or carcass or milk yield or composition? What about the sensory attributes (e.g., taste) of meat and milk from cows fed seaweed?

These uncertainties require attention because farmer income is derived from selling milk and its components (i.e, fat and protein) not by how much methane is reduced. Active research in this area at the University of New Hampshire is expected to provide clarity.

Although the Centers for Disease Control and Prevention states that bromoform is unlikely to be found in food for humans, bromoform consumption is a potential human safety concern. Research suggests that bromoform can be detected in milk from cows fed red seaweed at concentrations that would be deemed below the EPA-established maximum for drinking water. However, research from University of California, Davis, suggests that feeding cows red seaweed doesn’t impact bromoform content of meat. Scientific research on the matter is very limited but essential because the level of bromoform is highly variable across species of seaweed. So, the type but also the amount and duration of seaweed feeding are all critical factors that could contribute to bromoform content of animal-sourced foods but also the efficacy to reduce methane production.

Feeding cows seaweed is a potentially transformative approach to reduce methane production from the beef and dairy industries, but for it to become practice, we have some challenges to overcome.

Society has limited time to develop mitigation strategies for climate change. We must invest our time, people, and money with the conscious consideration of how technology will impact our environment, human health, and the livelihood of farmers.

Dr. Joseph W. McFadden is an associate professor of dairy cattle biology in the Department of Animal Science at Cornell University. He studies dairy cattle nutrition, milk production, and the effects of diets on animal and human health. His research — including current research on cattle methane emissions — is funded by USDA, NSF, FFAR and industry.