Creating waves of change: using seaweed to mitigate livestock methane emissions

Globally, agricultural production produces roughly one-third of all human-induced greenhouse gas (GHG) emissions (De Bhowmick and Hayes 2023). Livestock production - specifically cattle grazing - is often targeted as the main source of these emissions. A single cow can produce up to 3 tonnes of methane per year - a GHG that is up to 28 times more environmentally destructive than carbon dioxide (CO2) (De Bhowmick and Hayes 2023). Even though the ag industry provides food and essential nutrients to the global population and supports the livelihoods of 1.3 billion people (Davison et al. 2020), trends in global warming have raised concerns about the large quantity of these emissions, pressuring farmers to convert to more sustainable practices.

Changing the diet of ruminants (cattle, sheep, goats and buffalo) can alter enteric (intestinal) methane production and has been proposed as a solution to reduce GHG emissions. With this goal in mind, research has primarily focused on altering the antimicrobial, antioxidant activity and prebiotic potential of feedstocks (De Bhowmick and Hayes 2023). Feed ingredients vary globally depending on their regional availability and their compatibility with livestock species. Luckily, there is a diverse selection of ingredients capable of reducing livestock methane production. Patra (2011) lists these ingredients, including legumes, essential fats, oils and probiotics, among others. Because many of these ingredients are found in seaweeds, recent studies endorse seaweed as a viable ingredient for livestock methane reduction.

Ruminant methane production is a complex process that occurs within the animal's rumen. Ruminant livestock have specialised stomachs used to ferment plant material; the rumen is the largest chamber in the stomach. It contains a diverse community of bacteria, protozoa, bacteriophage and fungi, which help ferment and break down organic matter into volatile fatty acids and hydrogen (De Bhowmick and Hayes 2023). As a byproduct of this process, methanogens (methanogenic bacteria) then convert hydrogen, carbon dioxide or acetic acid in the rumen into methane, which is mainly released through belching (Davison et al. 2020).

Seaweeds are a diverse group of macroalgae (large algae) that can be categorised into three main types: brown, red and green algae. They contain mineral concentrations of up to 20 times that of terrestrial plants (Makkar et al. 2016). Commercial seaweed farming is considered the least destructive form of aquaculture to date. In fact, because of seaweeds' ability to sequester atmospheric CO2, reduce the occurrence of toxic algal blooms, lower nutrient concentrations (including nitrogen levels from pesticide run-off) and produce oxygen, the seaweed industry is pioneering environmental conservation (Maycock et al. 2023). In 2023, the seaweed market had an estimated value of US$60.5 billion and is expected to rise a further 7.8% between 2024 and 2032 (Global Market Insights 2024).

Seaweeds are a diverse group of macroalgae that contain mineral concentrations of up to 20 times that of terrestrial plants.

The use of seaweeds to feed livestock dates back at least as far as Ancient Greece and the Icelandic Sagas. Records show that seaweeds were also used as livestock feed in several European countries during the 19th and 20th centuries (Makkar et al. 2016). Today, 10 genera of seaweed comprise most of the seaweed market, which serves many global industry markets, including nutraceuticals, biomaterials and food and feed (Maycock et al. 2023).

As a feedstock, seaweeds have many benefits. Some of these are listed below.

• They are a source of complex carbohydrates and have a prebiotic effect (i.e., promote beneficial bacteria in the gut), thus improving the health of livestock (Øverland et al. 2018).
• They are a source of complex polysaccharides - chains of sugar molecules that improve energy storage, cellular communication, cell and tissue structure (Helmenstine 2020).
• They have high concentrations of crude protein - up to 50% in red algae and 30% in green algae (Makkar et al. 2016).
• They contain bioactive compounds that can be converted into secondary metabolites. Seaweed uses these compounds to fight bacteria in the ocean, but when added to ruminant feed, it blocks bacteria that produce methane (Wright 2023).
• They contain lipids, predominantly polyunsaturated omega-3, which is critical in developing a cow's central nervous and reproductive systems and has benefits to human health (Moallem 2018), and omega-6, which is shown to improve cow fertility and calf health (Cappellozza et al. 2021).
• They contain polymers such as alginates, which are beneficial for antioxidant, immune-regulation, anti-bacterial and anti-inflammatory activities (Liu et al. 2021).
• They contain compounds such as carrageenans, which improve gel formation and water retention in cattle, thus improving the texture of low-fat meat (Trius et al. 2009).

Several compounds, including saponins and phlorotannins, found in different seaweeds have been proposed to have methane-reducing capabilities in ruminants. However, the most successful and well-studied of these compounds is bromoform, which is mostly found in red algae. Due to its high concentration of bromoform, the genus Asparagopsis (native to Australia and other tropical and subtropical regions) is the most well-studied seaweed. Since the seaweed-feedstock industry is relatively new, understanding success rates and the potential effects of bromoform and other anti-methanogenic compounds is still very much in the developmental stage. Below are several studies proving the potential of bromoform as a feed supplement for ruminant livestock.

• Vucko et al. (2016) discovered that supplementing 1 mg g−1 dry weight of freeze-dried bromoform when added as 2% of organic matter to feed can stop methane production by 100%. While this research is a promising step towards sustainable ruminant farming, the study was completed in vitro (in a lab). As of yet, there is no in vivo research (performed on animals) that guarantees 100% inhibition of methane production.
• Kinley et al. (2020) had equally positive results after supplementing feed with Asparagopsis. Their study showed a 40% decrease in methane production when steer feed included 0.10% seaweed. When the amount of seaweed was increased to 0.20%, methane production was reduced by 98%. While many past studies highlight the potentially negative impacts of seaweed supplementation on animal health, Kinley et al. observed weight gain at 53% and 42%, respectively. They observed no changes in daily feed intake, rumen function or meat quality.
• Li et al. (2016) explored changes in methane production when introducing Asparagopsis in a pelleted form to sheep on a high-fibre diet. Their results showed an 80% decrease in methane production over a 72-day trial period when the seaweed was added as 3% organic matter.
• Roque et al. (2019) conducted the first anti-methanogenic study on lactating dairy cows. Methane production decreased by 67.2% when 1% of feed was supplemented with the seaweed. Although feed intake was reduced by 38%, they detected no changes in bromoform levels in the cows' milk.

Other seaweed genera have also been found to reduce methane production due to bioactive compounds such as tannins, polyphenols and oligosaccharides. In vitro studies on brown and green seaweeds have successfully reduced methane production by 20-45%, although in vivo studies have only shown a 10% reduction (De Bhowmick and Hayes 2023).

Like crops, individual seaweed species have specific requirements for adequate growth, including differences in water salinity, nutrients, temperature and light intensity (Makkar et al. 2016). The diet of ruminants is also unique to individual species and their external environmental factors. For example, studies have shown increased milk production and performance improvements in some ruminants, while the same seaweed decreased performance in others (De Bhowmick and Hayes 2023). Because feedstocks are species-dependent and vary across regions and climates, individual research by landholders is still necessary if considering incorporating seaweed into the diet of livestock. Overall, however, research suggests that for the best results, seaweed should be supplemented at concentrations of 0.5-2% dry matter in feed or above 1 mg g−1 of organic matter intake (De Bhowmick and Hayes 2023).

GreenFeed is an innovative device that accurately measures livestock methane and carbon dioxide production

Determining changes in methane production is more challenging than simply observing behavioural changes. Showcased at the 2024 Beef Week in North Queensland, GreenFeed is an innovative device that accurately measures livestock methane and carbon dioxide production. The mobile machine releases feed in pellets, attracting animals multiple times a day. It provides measurements for individual animals and averages for the herd before processing the data into easy-to-read reports via wifi or cellular connection. Data from each GreenFeed unit worldwide is also accessible online in real time and is already being used by Australian landholders.

As with all industries, there are limiting factors that must be considered before going 'all in'. Within the scientific community, the use of seaweed in feedstocks remains controversial, as some studies raise concerns that altering ruminant diets to reduce methane production may have adverse effects on animal health. The main concern is that reducing rumen fermentation will lead to reduced feed consumption, potentially risking livestock health (De Bhowmick and Hayes 2023). Studies have also shown that seaweeds accumulate heavy metals, including arsenic, which may impact animal health and humans consuming the meat (Makkar et al. 2016). Its antimicrobial activity can also impact rumen microbiota, leading to adverse changes in livestock health, including rumen mucosa deterioration, and the passing of bromoform into meat tissue, milk and blood (Munoz‐Tamayo et al. 2021). Several studies also highlight the potential impact of bromoform being released into the atmosphere and how this may negatively affect the ozone layer; however, this theory is disputed in other studies.

As research continues to explore the benefits and potential drawbacks of using seaweed for methane reduction, there is strong hope that this industry will soon develop into a lucrative global market.

Proudly Australian-owned, Sea Forest is the first company in the world to cultivate Asparagopsis and convert it into a feed supplement, which they've coined SeaFeed. Sea Forest are driven by scientific research and a desire to combat climate change while supporting Australia's cattle industry. Their sustainably produced seaweed is FAMI-QS certified and available in oil, pellet or lick block form.

Incorporating seaweed into feedstocks offers several compelling benefits. Most importantly, its potential to reduce GHG emissions could significantly relieve pressure on livestock producers who face ongoing criticism for their environmental impact. Additionally, seaweed is a highly nutritious feed source that can provide essential nutrients that might be missing from livestock's diet. However, if you're considering seaweed as a feed supplement, it's crucial to conduct thorough research to ensure the best outcome for both the environment and the health of your livestock. Finding a balance between methane reduction and animal wellbeing is essential.