Field tests less conclusive than studies and less effective over time, carcinogenic active agent: feed additives reducing methane emissions from livestock, such as red algae or 3-NOP, have their limits, believes a group of experts. Based on several studies, this panel of five academics and researchers identified in a document published on May 18 the advantages and disadvantages of these food supplements which are attracting the interest of farmers and governments eager to lower their methane emissions.

Livestock production is responsible for around 12% of human-caused greenhouse gas emissions, largely through releases of methane, the second-largest warming gas behind carbon dioxide (CO2). This is mainly due to the digestive process of ruminants releasing methane through belching. Faced with this observation, some are trying to change their cows’ diet: replacing part of their diet with a type of red algae would, for example, reduce their methane emissions by more than 80%, according to a 2021 American study.

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An effectiveness called into question by this group of experts. If red algae reduced methane emissions by up to 99% in the laboratory, the most extensive field study only revealed a 28% reduction in Japanese livestock, which had otherwise lost weight at the end of the trials. Scientists also point out that the active ingredient in red algae is bromoform, a known carcinogen for animals and possibly humans. Already used by the French giant Bel, manufacturer of Babybel, Boursin and Kiri cheeses, 3-NOP (3-nitrooxypropanol), marketed under the name Bovaer, is faring better.

Made by heating nitrate and a vegetable alcohol, this additive in powder form reduces methane emissions from ruminants by 30% on average, with better results in dairy cows. However, some long-term trials have shown it to be less effective over time. Experts also point out that there is currently no effective way to regularly provide nutritional supplements to grazing animals.

The panel is composed of Ngonidzashe Chirinda of the Mohammed VI Polytechnic University in Morocco, Mark Howden of the Australian National University and Andy Reisinger of the New Zealand Climate Change Commission, all three of whom participated in the work of the intergovernmental group experts on climate change (IPCC). Also participating were Mario Herrero of Cornell University in the United States and Claudia Arndt of the International Livestock Research Institute in Kenya.