Seaweed as a methane inhibitor is not free of risks

March 12, 2021

Cows exhale the strong greenhouse gas methane. One of the possible ways to limit methane emissions from cows is by feeding them the seaweed Asparagopsis taxiformis. This seaweed contains high concentrations of bromoform, a substance that counteracts the formation of methane in the cow's rumen. Research by Wageningen University & Research (WUR) shows that bromoform can then end up in the milk and urine of the cow.

“Bromoform inhibits the formation of methane in the cow's rumen. However, it is also toxic. ”, says Wouter Muizelaar, researcher at Wageningen Livestock Research. Previous research linked A. taxiformis to abnormalities in the rumen wall of sheep. “That is why we wanted to know what effect A. taxiformis has on cows. Does bromoform end up in milk, urine, manure or animal tissue? What happens with it? This research shows that bromoform from A. taxiformis can end up in milk and urine. A clear indication to reconsider whether it is desirable to feed this type of seaweed to cows.” 

Long-term effect unknown 

The rumen wall of 2 of the 12 cows was examined and, as in sheep, this revealed abnormalities and signs of inflammation. This worries Muizelaar: “Bromoform in its pure form is harmful to health. Previous research has already shown this. It is not without reason that there are limits for the maximum amount of bromoform in drinking water. There are no such limits for food. The fact that the substance can now also be found in the milk is extra worrying. Food safety must always be above any form of doubt. ” The researcher therefore emphasizes that there is currently no milk containing bromoform in Dutch supermarkets. The milk from this study has been destroyed.


Muizelaar concludes that the bromoform-containing seaweed can greatly reduce the methane emission of cows, but expresses the need for further research; to rule out negative effects for cows and consumers.

Asparagopsis taxiformis 

This research focused on the specific seaweed species Asparagopsis taxiformis, because it contains concentrated amounts of bromoform. Now that the use of this type of seaweed raises all kinds of questions, the obvious question is whether you should feed seaweed to cows at all. Muizelaar explains that other seaweed species contain less or no bromoform, but may also reduce methane. “They work slightly differently because they contain other methane inhibiting compounds. So I still see seaweed as a promising option that we should continue to explore. ”

Methane research 

WUR has been researching ways to reduce or prevent methane formation in livestock farming for years. For example, we are investigating, on behalf of the Ministry of Agriculture, Nature and Food Quality which measures can be taken regarding animal feed, animals, stables and manure storage. More information about this can be found on

This research was commissioned and funded by: ProSeaweed, BluGrass and the Dutch Ministry of Agriculture, Nature and Food Quality. 

This research is described in more detail in the scientific journal Foods