Weight for weight methane causes 36 times as much global warming as carbon dioxide and the main sources of this pollutant is agriculture. Farm animals produce 3.1 gigatonnes of methane in burps (95 per cent) and farts (five per cent) worldwide.
Now scientists have found that making the diet contain just 2 per cent of dried seaweed could reduce this by more than 70 per cent.
Farmers on the Atlantic coast of Canada have been feeding storm-tossed seaweeds to cattle as a source of minerals for generations. The seaweed has been fed without reported ill effect on animals and with unanimous, however anecdotal, feeling among farmers that this is beneficial to animal health.
Seaweeds are also known as macroalgae. They are widely used in the nutrachemical and health markets and have anti-bacterial, antiviral and anti-inflammatory properties. They are also common ingredients in many human cuisines and consumed by many cultures in many countries.
In a classic example of serendipity, Canadian researcher Dr Rob Kinley, now working for CSIRO in Australia, found that feeding those storm-tossed seaweeds to cattle also reduced methane production by 20 per cent.
Since then, and supported by Meat and Livestock Australia, Dr Kinley along with Rocky de Nys, professor of aquaculture at James Cook University (JCU) in Townsville, have tested more than 20 species of seaweed for efficacy in reducing methane productions in an artificial rumen.
The seaweed species tested reduced methane production in laboratory cultures from cow rumens by anything from zero to 50 per cent. But with many of the seaweeds to achieve this result required large amounts of seaweeds which is costly, unsustainable, and has potential to present digestion issues for animals that could result in loss of productivity. "We started with 20 species [of seaweed] and we very quickly narrowed that down to one really stand-out species of red seaweed," Dr Kinley said. That is the red algae Asparagopsis taxiformis.
When the researchers tested this seaweed, collected from Queensland's coastal waters, the results were so over the top they ran the tests again. It turns out that it reduced methane production by more than 99 per cent in the lab. And unlike other seaweeds, this species works at inclusion rates of less than two per cent.
Since then JCU researchers under permit have been collecting limited quantities of this species off the coast of Queensland. It is washed in clean seawater and dried and incorporated in experimental diets along with familiar feeds such as crushed lupins for sheep and steam flaked barley for beef cattle.
Michael Battaglia from CSIRO said it turned out the reason this particular type of seaweed was so effective was because it produced a compound called bromoform (CHBr3), which blocked microbial methane production by reacting with vitamin B12 at the last step in the formation of methane in the rumen. "This disrupts the enzymes used by gut microbes that produce methane gas as waste during digestion," he said.
The inclusion of Asparagopsis in the daily ration of sheep resulted in a small decrease in acetate and total volatile fatty acid production and an increase in propionate. However, liver function was not adversely affected by the treatment.
Dr Kinley told the ABC that all sectors of agriculture were trying to be responsible and reduce their contribution to climate change, which in many instances related to reducing their contributions to greenhouse gas emissions.
"Agriculture stands to be one of the first to make dramatic reductions if we can get this to market," he said.
However, while their research was promising, Dr Kinley said there was no current large-scale and consistent access to this seaweed.
"That is the number one barrier ù getting enough seaweed to feed to millions of cows," he said. "Wild harvesting isn't going to do it because it's far too expensive and the resources aren't enough, so we need to get partners on board who can produce the seaweed in a cultivation process.
"Whether that be in South-East Asia where they are already farming millions of tonnes of seaweed, or beginning a new industry somewhere through the southern or western side of Australia."
Although, according to Dr Kinley, time was less critical than money in this case. "Money will decide how quickly we can move ... the sooner we have more money to move forward with the research, the sooner we will be able to get it out," he said.
"Three years isn't outside the realm if we can get enough support to move with it."
Dr Battaglia said if seaweed feed could be included as a treatment under the Emissions Reduction Fund, carbon credits might be available from it.
Deputy director of the New Zealand Agricultural Greenhouse Gas research centre, Dr Andy Reisinger, said seaweed production of bromoform would present a high risk of bromoform leakage into the atmosphere, which would be impossible to control fully in a seaweed farm.
He also said that if bromoform leaked into the atmosphere it could contribute to a reduction of the earth's protective ozone layer.
Dr Kinley pointed out that bromoform was produced naturally in seaweed, had been for millions of years and was mostly released when the seaweed decayed.
Seaweed was not concentrated bromoform and was safe to transport and store without concern for spills and leakage.
Harvesting and feeding seaweed was a different pathway that might destroy much of the bromoform and should not increase the amount of bromoform released to environment as if it was simply left to decay in the ocean.
This is a feature that needed to be quantified in upcoming studies as the researchers tracked the biological processes, Dr Kinley said.
"If 10 per cent of Australian feedlot and dairy cattle were fed seaweed it would only increase the contribution to atmospheric bromoform produced by seaweed by 0.04 per cent if all the bromoform in the seaweed was able to escape," he said.
"The environmental benefits in methane reduction should greatly exceed any environmental cost."
NZ's Dr Reisinger said the main mitigation effect did not come from seaweed as such but from the bromoform that the seaweed contained.
"Because it was a simple enough chemical to produce in a laboratory it would be easier to administer it to animals via a bolus rather than go to the trouble of growing seaweed," he said.
"That would allow much more accurate dosing and avoid all the potential negative environmental side effects of large-scale seaweed production."
But the CSIRO team said it was keen to be seen to be using natural substances when producing food for human consumption. Feeding seaweed was acceptable to organic farmers, while feeding bromoform as a pure chemical was not.
NZ's Dr Reisinger also raises concerns due to the potential for the chemical to turn up as a residue in food where it is regarded as a possible carcinogen.
But Dr Kinley refuted this. "I've only been able to find one study where mice force fed 1200 times the dose received in the seaweed developed tumours," he said. "At that dosage anything would cause problems.
"Cattle will only receive seaweed for a short period of their lives and at much lower doses."
CSIRO trials with sheep found no detectable levels of bromoform in fat or muscle samples and the sheep did not appear to be affected by either bromoform toxicity or metabolic acidosis as a result of feeding seaweed. "This aspect will be stringently monitored in our research and food safety and security is as always the foremost objective," Dr Kinley said.D