Climate Change

Burp control: How can methane released in livestock belches be reduced? Scientists are trying various options

Scientists are experimenting with seaweed as well as concoctions having several other ingredients to make the specialised digestive system of livestock release less methane; but much still needs to be done

By Rohini Krishnamurthy
Published: Sunday 18 December 2022

Photo: Avijit DeyAvijit Dey and his colleagues at the Central Institute for Research on Buffaloes in Haryana, have spent the past 15 years developing and perfecting a formula that could potentially help the world from getting ever hotter.

They have prepared a feed supplement that can reduce a potent greenhouse gas belched out by stock animals like cattle, goat and sheep.

Yes, just like fossil-fuel infrastructure and coal mining, ruminants also release methane, the second most abundant greenhouse gas after carbon dioxide (CO2), which is seen as the biggest concern as well as the best opportunity for tackling global warming.

Although the warming effect of methane is 30 times greater than CO2, it is shorter-lived and lasts in the atmosphere for about 12 years.

By contrast, CO2 lingers for centuries. Reducing methane emissions has therefore been touted as one of the most immediate opportunities to slow global heating.

In 2021, over 100 countries signed the Global Methane Pledge, where signatories agreed to take voluntary steps to reduce global methane emissions by 30 per cent from 2020 levels by the end of the decade.

This, they say, could eliminate over 0.2˚C warming by 2050.

The US National Oceanic and Atmospheric Administration says human activity alone emitted 640 million tonnes of methane in 2021.

Dey and scientists across the globe are placing their bets on diet supplements to help bring down the emissions.

“I think we are going to be heavily reliant on feed supplements to reduce methane emissions,” Ermias Kebreab, director, World Food Center, and professor and Sesnon Endowed Chair, University of California, Davis, told Down To Earth.

In a 2021 study published in the journal Philosophical Transactions of the Royal Society, researchers from New Zealand, Australia and the US write it is technically possible to reduce emissions from enteric fermentation to 50 million tonnes per year by 2050.

Diet check

The science of abating methane emissions with the help of feed supplements is fairly straightforward.

Unlike other animals, ruminants have specialised digestive systems comprised of stomachs that have four compartments instead of one.

Plant material is initially taken to rumen, the largest compartment in the stomach that is inhabited by microorganisms such as fungi, bacteria, protozoa and archaea.

These microorganisms break down the otherwise indigestible cellulose-rich plants to release protein and energy for their host animal in exchange for nutrition and shelter.

But during this process, which scientists call enteric fermentation, one particular microbe, the archaea, combines CO2 and hydrogen made by the cellulose-digesting microbes to create methane. This means the archaeal population and a diet rich in roughages dictate the amount of methane released by a ruminant.

Read Methane emissions from fossil fuels much higher than current estimates

The feed supplement prepared by Dey and his team thus targets the archaeal population, while boosting the growth of bacteria that are good at digesting feed.

The supplement is a concoction of ingredients such as Indian cherry and Indian elm leaves, garlic oil, mustard oil, cottonseed oil, sodium nitrate and magnesium sulphate.

While tree leaves possess compounds like saponins and tannins that are known to reduce archaeal population and cut off hydrogen supply to them, sodium nitrate and magnesium sulphate stimulate the growth of beneficial bacteria.

When given individually, these chemicals must be administered in high doses to have a measurable impact on the archaea. They also affect beneficial microbes, hampering digestion and animal productivity, such as milk or meat production.

So Dey and his team decided to combine the ingredients. With composite food additives, the dose of individual components is lower, giving beneficial microbes a free pass.

To measure efficacy of the feed supplement and the best dose for optimal results, the researchers initially conducted laboratory tests, where they mimicked the rumen by mixing rumen fluid collected from a buffalo with the composite supplement.

Since many rumen microbes may not survive in the laboratory, in 2016, they initiated another experiment involving calves aged 1-1.5 years. The team put Murah calves, a buffalo breed predominantly found in Punjab, Haryana and Delhi, on a six-month-long diet consisting of 2-3 kg of concentrate feed and 10 g of composite supplement per day.

During this period, the researchers fixed an inflatable gas-collecting bag onto the mouths of the calves, before and after they ate the meal, to collect exhaled air. Laboratory analysis showed that methane emissions dropped by 75 per cent. The calves also recorded a 9.7 per cent higher growth rate.

In 2018, Dey expanded the experiment to include lactating animals and fed them 6-6.5 kg of concentrate feed mixed with 50 g of the composite supplement per day for three months. From the exhaled air, the team recorded a 44.6 per cent decrease in methane concentration.

A food supplement is considered ideal if it can lower methane emissions by at least 20 per cent, said Alexander N Hristov, distinguished professor of dairy nutrition at the Pennsylvania State University, US. Early this year, Dey and his colleagues received a patent for the supplement. “Our next step is to seek regulatory approval, followed by commercialisation,” Dey said.

Since ruminants can be picky eaters, Dey and his team gradually introduced the feed additives. “On the first day, we give 10 g and maintain this for three-four days before we increase it to 20 g for the next four days. We continue this until we reach the actual dose of 50 g,” said Dey.

Though he tested the supplement on one of the 17 buffalo breeds found in India, he argues that the product could be effective on other breeds and cows as digestive tracts of ruminants and their microbial inhabitants are similar.

Seaweed, an option

Globally, there is a race to develop different strategies to reduce methane production in ruminants. In 2021, the EU approved a feed supplement, Bovaer, developed by Dutch bioscience company Royal DSM, saying it consistently reduces methane emissions from dairy cows by 30-80 per cent.

Bovaer is a fine granular powder containing 3-nitrooxypropanol, which inhibits an essential enzyme responsible for methane production. Some experts are placing their bets on seaweed, particularly Asparagopsis taxiformis, a red alga growing in tropical and subtropical waters.

In 2017-18, Matthias Hess, associate professor of animal science at the University of California, Davis conducted a laboratory study using Asparagopsis taxiformis and recorded a 95 per cent decline in methane production.

The seaweed supplement could be commercially available in a few years; but Hess is not sure if the response will be similar for all animals.

Experiments on cattle have also yielded encouraging results. Kerbreab’s 2021 study published in PLOS One records an 80 per cent decline in methane emissions in cattle raised for beef production. They do not have any health effects and meat quality is intact.

People could not detect any difference between cattle fed a seaweed diet and those on a regular diet. A follow-up study, to be published soon, corroborates these findings.

Hess and his colleagues dived deeper into the rumen, looking at changes in gene expression, where instructions in the organism’s DNA are converted into proteins.

The seaweed did not displace microbes from the rumen, but they may have become less active. “The animal does not want to get rid of those microbes because they might need them again later,” he said.

Hess stressed that it is important for countries to rely on local ingredients. “The problem is the supply chain. Even if the supply chain works well, one cannot ship seaweed from Australia to the US to reduce methane, given the higher carbon footprint of the shipping sectors,” he said, adding that local species should be evaluated.

So, his team conducted laboratory tests on locally sourced Asparagopsis taxiformis and brown seaweed Zonaria farlowii. The two species reduced methane emissions by 74 per cent and 11 per cent, respectively, as per their findings published in 2020 in Frontiers in Marine Science. “It is not as high as Australian seaweed but still decent. The bottom line is, we are eliminating shipping emissions,” he observed.

A few issues exist. Seaweed appears to inhibit release of greenhouse gases through two chemicals, bromoform and bromochloromethane, which can induce cancer. Residues of the chemicals have been detected in milk and urine of cows fed seaweed. More studies are needed to evaluate this concern.

Ruminants also appear to dislike seaweed. “It has an objectionable odour,” said Hristov. Kebreab added that feeding bovines smaller quantities of seaweed, say, less than 100 g for dairy cattle, can help. Watson overcame this problem by mixing the seaweed supplement with distiller grains, a byproduct of ethanol production.

Regulatory procedures could also be a hurdle, particularly in the US, where feed is treated as a drug, said Watson. The product is vetted thoroughly and could take at least five years to get regulatory approval.

There are other concerns stemming from an incomplete understanding of rumen microbes, such as the possibility of them developing resistance to the supplement.

“Understanding the microbiome to predict how microbes respond to the supplement is essential and will help prevent resistance or develop alternative strategies,” said Watson.

But these organisms are notoriously hard to study in the laboratory. They are sensitive to oxygen, and nutrients provided to them in laboratory conditions might not be conducive to their growth. “There is still much work to do,” said Hess.

This was first published in the November 16-30, 2022 edition of Down To Earth

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