Seaweeds contain substances that can reduce methane production in the rumen of ruminants. The content of these substances varies throughout the year, research shows. Photo: Ingebjørg Hestvik
This result came from an in vitro rumen fermentation study in which a seaweed-feed mixture was exposed to cow rumen fluid.
Ruminants, such as cows, sheep, and goats, have a 4-chambered stomach, where the rumen is the biggest component. The rumen contains a unique set of a microorganisms. These microorganisms play an important role in feed digestion, but some of them also produce methane gas. Methane is a potent greenhouse gas with high global warming potential, and therefore, methane production from ruminants causes a negative impact on the environment.
To reduce greenhouse gas emissions, there has been a strong focus in recent years on finding alternative feed supplements that can be directly added to the ruminant diet.
12 Norwegian species controlled
A few marine macroalgae (seaweeds) - particularly the red tropical alga Asparogopsis – have already shown promising results. However, little is known about whether Nordic or Norwegian macroalgae also have this enteric methane mitigating potential. Researchers from Nord University, Norway, University of Copenhagen, and Aarhus University, Denmark, performed an extensive study to explore the potential of 12 norwegian seaweed species as animal feed ingredients, together with their seasonal variations in nutritional composition and ability to reduce enteric methane production.
“Macroalgae contain certain special substances, also called bioactive compounds, which help them survive and defend themselves in the harsh environmental conditions in the sea. These compounds can change the composition and activity of microorganisms living in the rumen of ruminants. This includes methanogenic microorganisms that produces methane gas", explains researcher Deepak Pandey, a former PhD fellow at Nord University.
Pandey recently completed his doctorate at Nord University, where he studied marine macroalgae as an alternative, environment friendly and health-promoting nutrient source for livestock.
“By adding 20 percent of the algae to the feed and fermenting it using rumen fluid from cow stomach, we found that some of the macroalgae harvested from the Norwegian coast were able to reduce methane emissions. One of the most important species, Fucus vesiculosus, reduced methane emissions by as much as 62 percent,” says Pandey.
Fucus vesiculosus grows in large quantities along the entire Norwegian coast. In addition to F. vesiculosus, another brown alga that can easily be confused with bladderwrack is knotted wrack (Ascophyllum nodosum). This alga also contributed significantly to reducing methane production in the feed experiments.
Unique polyphenols
Both these brown macroalgae have a common property. They are rich in bioactive compounds, particularly polyphenols or phlorotannin.
“These are substances that algae produce to defend themselves against adverse climatic conditions such as exposure to sunlight. These substances have several beneficial properties for health and work as antimicrobials and antioxidants, says Associate professor at Nord University’s Faculty of Biosciences and Aquaculture, Prabhat Khanal.
In the study, researchers found that a high polyphenol content was linked to methane-reducing property of the macroalgae. However, they also found that the reduction in methane gas was associated with lover feed digestibility. In the in vitro rumen fermentation study, bladderwrack and knotted wrack resulted in a 25 percent reduction in feed digestibility with 20 percent inclusion in the feed.
Thus, the climate benefit of the macroalgae may come at the expense of feed digestibility and utilization.
“Microorganisms help digest the food. But not all have such a useful role for the animal. Some microorganisms digest carbohydrates, while others only produce methane. What happened was that the methane-producing microorganisms were reduced, but the bacteria responsible for feed degredation were also affected,” says researcher Pandey.
Therefore, the ideal situation would be to find a feed resource that inhibits only the methane-producing microorganisms without compromising feed digestibility and utilization.
“The question then becomes: How much algae should be added to the feed? And which types? This depends not only on the methane reducing property of algae, but also on their nutritive values and effect on feed digestion”.
Certain other species, like the green alga Ulva lactuca, also led to a high level of reduction in enteric methane, more than 30 percent compared to the control diet without macroalgae. Moreover, unlike most brown macroalgae, the green alga has a high protein content.
“Even though the methane reduction is not as high as 60 percent, it is an important finding. If we can reduce methane production by “only” 30 percent, it would still have a significant impact on greenhouse gas emissions”, says Associate Professor Khanal.
An underutilized resource
He emphasizes that the economic side of using macroalgae in livestock production must also be considered.
“Seaweeds are underutilized and are good sources of nutrients and bioactive compounds, but the question is whether their commercial production is economically sustainable. Can it increase the profitability of farmers? This is something that always must be included in the calculations,” says Khanal.
Researchers at Nord University have also compared the nutrient content of Norwegian brown algae at different times of the year. Harvesting the algae in the spring results in a higher protein content than in the fall. However, the content of polyphenols is higher in the fall than in the spring.
“This is important knowledge to have when harvesting the seaweed. One must choose the season based on what the seaweed will be used for,” says Khanal.
Seaweeds and kelps have been difficult to use as animal feed, as they contain certain carbohydrates that are difficult to digest. Brown algae also have high levels of minerals such as iodine, phosphorus, and sodium that can limit their use in the feed.
“Animals need a number of minerals, but too high mineral intake can have negative effects. However, the minerals can be reduced in macroalgal biomass by certain post-harvesting processing, such as hot-water blanching. Such simple processing of macroalgae biomass can increase their safety as animal feed. But again, we need to consider sustainability, both economically and environmentally,” says Khanal.
In other words, more research is needed before the environmental benefits of marine algae can be utilized. At Nord University, Khanal and other researchers aim to develop new projects by taking the experiments out of the laboratory and into the barn.
“But first, we need to conduct more laboratory experiments. So far, we have harvested seaweeds in the spring and fall, but we also want to look at the summer season. Once we study the seaweeds from the three seasons in the laboratory, we can move on to large-scale feed experiments on animals,” says Khanal.
The research was funded by Nord University and the Regional Research Fund Trøndelag. Nord University was project owner whereas the University of Copenhagen (UCPH) and Leica AS were project partners.
