To fully understand the subject and the role that algae can play in reducing enteric methane, it is important to know that methane is produced by bacteria in the cow’s rumen (the first stomach of ruminants). Certain metabolic pathways of these bacteria, which are necessary for digestion in the animal, lead to the production of methane, which is then eroded and released into the atmosphere.
Algae contain various molecules with antimethanogenic properties
Algae live in the marine environment, which, like the terrestrial environment, contains its share of fungi, bacteria and viruses. Algae have therefore developed a whole range of molecules to defend themselves, particularly against bacteria: halogenated derivatives, phenolic derivatives, polysaccharides, terpenes and terpenoids, fatty acid derivatives, pigments, etc.
In the case of methane reduction, it is mainly halogenated derivatives and polyphenols that show interesting effects. Halogenated derivatives work by diverting the metabolic pathways of digestion that usually lead to methane production. This is the type of molecule found in Asparagopsis sp., which contains high levels of bromoform. Polyphenols (e.g. phlorotannins) act directly on bacteria with a strong antibacterial effect.
Interesting in vitro results
Various scientific studies have investigated the effect of algae on methane reduction in vitro using fermenters containing rumen juice that can mimic rumen digestion. Asparagopsis sp. has of course been the subject of the largest number of publications. In recent years, new publications have appeared on other species of algae, in particular brown algae (Ascophyllum nodosum, Saccharina latissima, Alaria esculenta, Fucus sp., etc.) and some red algae (Chondrus crispus, Grarcilaria sp., etc.).
The criteria looked at in these trials are, of course, the reduction in methane production, but also the impact on digestion, particularly the production of volatile fatty acids (VFA), an essential source of energy for ruminants. In fact, reducing enteric methane is worthwhile if it does not lead to excessive disruption of digestion, which could be detrimental to the animals’ well-being and performance.
The in vitro results are variable depending on the species. Asparagopsis sp. is the species with the greatest reduction in methane (up to 100%) depending on the incorporation rate applied. On the other hand, and particularly at the highest rates, Asparagopsis sp. has a negative impact on digestion, with a reduction in VFA production.
For the other species tested, the results varied widely depending on the species and the incorporation rate (from 6 to 100%). The impact on digestion also varied according to the same criteria.
A more difficult transition to in vivo
Despite interesting in vitro results, these are not systematically repeated in vivo. Asparagopsis sp. does reduce methane in suckler cattle (by up to 98%), although it does have an impact on animal digestion. It is by far the most interesting species in this respect, although these effects have not always been found in dairy cows and small ruminants.
Other species (e.g. Chondrus crispus, Saccharina latissima, Fucus serratus) that have been tested in vivo do not reproduce the effects observed in vivo. In collaboration with various partners in the sector, CEVA has carried out a project (https://www.ceva-algues.com/document/le-projet-methalgues/) where similar results were found.
What are the prospects for algae in methane reduction?
At present, the most promising algal species for reducing the methane produced by ruminants is Asparagopsis sp. This is the species that shows the greatest reduction effects and, above all, that is reproduced on an in vivo scale. However, before this discovery, this species was only marginally cultivated. Even though a number of start-ups have embarked on growing it at sea or on land (e.g. Blue Ocean Barns, CH4Global, Voltagreen Tech, Algues & Mer), large-scale production is still not guaranteed to feed the world’s entire livestock population.
There is also a logistical issue to ensure that the seaweed is ingested under optimum conditions. To be sure of ingestion, the seaweed is distributed at the trough in the livestock buildings. However, the cattle spend part of their time on pasture, with periods spent exclusively outdoors, where it is still complicated to control feeding, which is done in groups when grass supplements are provided.
Finally, analyses of the bromoform molecule are still needed to determine its potential impact on animals and the environment. Initial studies on bromoform residues in animal products (milk, meat) show that there are none, which is essential to reassure consumers. However, studies are still needed to assess the environmental impact of this molecule, particularly in the atmosphere and on the ozone layer. Similarly, the safety of this molecule for animals remains to be demonstrated, as does its long-term action in reducing enteric methane: in fact, the rumen microbiome adapts to the conditions it is given. It is therefore possible for parallel metabolic pathways to develop over time, leading to an increase in methane production.