By Veronika Meduna Veronika.Meduna@radionz.co.nz
The programme has been looking for new types of inhibitors of methane production from the rumen. This can be regarded as a first step in the process towards developing something that can be used on the farm. Peter Janssen, AgResearch
A team of AgResearch scientists has identified five compounds that reduce methane emissions from livestock by up to 90 per cent in initial short-term trials, providing a technology that could significantly reduce New Zealand’s greenhouse gas emissions.
New Zealand is unusual among developed countries in that almost half of the country’s greenhouse gas emissions come from agriculture, mostly in the form of methane from belching livestock and nitrous oxide from fertilised soils. Methane is a potent greenhouse gas and currently accounts for 44 per cent of New Zealand’s total emissions. Most of this methane comes from livestock.
AgResearch principal scientist Peter Janssen, who coordinates the methane research programme, says the findings are the culmination of five years of work, during which the team screened more than 100,000 compounds through computer-based searches and in laboratory experiments. The screening process identified five compounds that have now been tested successfully in sheep, showing a significant reduction in methane production over a two-day period.
The rumen is the first and largest part of the multi-chambered stomach of grass-eating ruminant animals, including sheep and cattle. It acts as a fermentation vat where microbes break down the cellulose in the plant material to make it digestible. One group of rumen microbes, the methanogens, takes up surplus hydrogen and produces methane.
In recognition of the fact that methane accounts for most of New Zealand’s agricultural greenhouse gas emissions, several research organisations have formed the NZ Agricultural Greenhouse Gas Research Centre, hosted by AgResearch, in 2009 to investigate ways of mitigating emissions of greenhouse gases other than carbon dioxide. Even earlier in 2003, the government and the pastoral industry had formed the Pastoral Greenhouse Gas Research Consortium which funded some of the fundamental research to sequence the methanogen genome and to identify targets for inhibitors. Peter Janssen says the effort is now paying off.
These initial steps are relatively short-term trials in sheep and they show that you get a reduction of methane between 30 to 90 per cent. It’s a very exciting result but there’s still a lot of checking to be done before you actually get something that a farmer can use safely.
AgResearch scientist Ron Ronimus, who leads the methane inhibitor discovery project, says the team made use of genetic information that became available when the first complete genome of a methanogen was published in 2010. Of the roughly 500 known genes, the team focused on finding compounds that would inhibit the function of those that are known to be involved in the production of methane.
Methanogens belong to a group of ancient microbes known as archaea, and that is an advantage. “They are very different from other bacteria, protozoa and fungi that are also in the rumen, breaking down the fibre during the fermentation.”
The team scaled up the discovery process by screening thousands of potential compounds in the laboratory and then testing the most promising inhibitors in sealed containers of real rumen fluid.
“It’s a very thick funnel if you like, we’re putting many compounds in at the top and getting very few out at the bottom.”
Each of the five compounds had to pass toxicity tests before they could be tested in sheep in respiration chambers that allow the science team to monitor changes in methane emissions precisely, as well as feed intake.
“The intention is to only hit the methanogens,” says Peter Janssen. “The nice thing about the way the programme is structured is that the last major test before the compounds go into the animal is to test them in rumen contents that have been taken from an animal.
If it has a general impact on other microbes in the system, then you see that the whole fermentation shuts down. If it’s only affecting the methanogens then you see that the fermentation continues just like normal, and it’s only the methane part that is affected. If it then passes subsequent toxicity testing then we know we can safely try it in an animal.
The team will now test if the inhibition effect lasts long-term and whether it could even be used to increase animal productivity.
Earlier research suggests that methanogens are not an essential part of the rumen microbial community, but rather opportunists that make use of surplus hydrogen that is a by-product of the fermentation process.
“Certainly when you knock out the methanogens in experiments we’ve done to date the animal seems to carry on eating and seems to be ok, and all of the published studies suggest that the methanogens don’t seem to be essential. They are just really good at surviving there [in the rumen] and they take a cut of the energy.”
In fact, methanogens take up to 15 per cent of the energy that could otherwise be available to the animal, and the team hopes to recapture some of that loss. An ideal outcome of the research would be both a reduction in methane emissions and an increase in productivity.
The team says that apart from monitoring such desired effects, larger-scale trials are also necessary to rule out any negative effects such as residues in meat or milk. Ron Ronimus says residues may not be an issue as the compounds have already been preselected to be non-toxic and not soluble in fat so that they don’t accumulate in milk. “They are also easily metabolised and quickly eliminated, and of course specific to methanogens. A combination of these properties and aiming for the most highly potent compound, which reduces the concentration that you’ll need sometimes by orders of magnitude, the residue issue will not be a problem.”
One of the strategies to deal with the possibility that the methanogens become resistant to the inhibitor treatments is to develop a suite of compounds that would be used simultaneously to override the ability of the microbes to adapt.
The team’s goal is to have a farm-scale product available or at least close to commercialisation within five years.
“We think we can do this,” says Peter Janssen. “The fact that the programme, which really only started about five years ago, this inhibitor discovery … has come up with pretty much the first five that were tested in animals look pretty good. I think there is a very good chance of coming up with something that will be useful.”
The search for methanogen inhibitors is one of four main strategies to develop new technologies to reduce methane emissions from livestock in New Zealand. Others are to develop a vaccine, to breed for naturally low-emitting animals and to find feeds that result in less methane being produced.
Peter Jansen describes the latter two as “almost sure bet but small impact”.
“They are really worth doing because they probably going to work. We know that these things can work and the programmes are very well advanced. Two other projects funders have backed are much more technically difficult … but their impacts are much greater.”
With the progress made in identifying methanogen inhibitors, he says we “could be talking potentially 90 per cent methane reduction, which would be an enormous impact on New Zealand’s greenhouse gas footprint”.