The world is a step closer to a low-emission sheep, thanks to leading work by Kiwi and US researchers.
Methane belched from sheep and other ruminants, such as cows, accounts for around 28 per cent of global methane emissions from human-related activities.
The methane is produced in the rumen by microbes called methanogens and the work targeting these organisms is aimed at reducing methane emissions from ruminants.
New Zealand has the largest methane emission rate -- six times the global average -- and this primarily comes from enteric fermentation in ruminant livestock, with sheep the greatest single source.
Research published today shows scientists have pin-pointed the microbial differences in the rumens of sheep with high or low methane emissions.
The work is part of a Global Partnerships in Livestock Emissions Research project and has been carried out by the Rumen Microbiology team at AgResearch Grasslands in Palmerston North, and at the US Department of Energy's Joint Genome Institute (JGI) in San Francisco.
AgResearch scientist and project leader Dr Graeme Attwood said the results, revealed in the journal Genome Research, were one of the first major findings of the four-year project.
"The study used the large sequencing and data analysis capabilities of the JGI to look at the occurrence, abundance and expression of methanogen genes between low and high methane-emitting sheep identified from flocks in New Zealand," he said.
"These analyses showed that, although the relative abundance of genes did not differ between the low and high methane groups, the expression of genes involved in the metabolic pathway leading to methane formation were significantly elevated in methanogens within the rumens of high methane-emitting animals."
This discovery helped explain the methanogen involvement in this animal trait, and it was likely that further detailed analysis of the large sequence datasets would uncover differences in other rumen microbes which also contribute.
The study was funded through the New Zealand Government in support of the objectives of the Global Research Alliance on Agricultural Greenhouse Gases and its Livestock Research Group, and built on previous work by a combined New Zealand Agricultural Greenhouse Gas Research Centre (NZAGGRC) and NZ Pastoral Greenhouse Gas Research Consortium programme in which a large number of sheep had been screened to identify naturally low or high methane-emitting animals.
The programme aimed to breed sheep for New Zealand farms which are low methane-emitters but also maintain their ability to reproduce and retain or improve their meat and wool production.
The microbial gene expression differences discovered in the study help define the methane trait in sheep and will assist in the selection of future low methane flocks.
"Understanding the microbial composition of a low methane animal and how its rumen works, will enable us to focus on targeting the methanogens directly using complementary approaches such as drenches, slow release boluses or specialised forages and supplements," Dr Attwood said.
Meanwhile, scientists are also looking at how to slash the methane emitted from cows.
NZADGGRC deputy director Dr Andy Resinger told the Herald earlier this year: "The problem right now is cows produce methane because that's just part of how they function and we can't change that -- yet." While farmers had slashed per-unit greenhouse gas emissions, largely from making improvements to farm efficiency and productivity, total emissions had risen as the dairy industry had grown.
One area of research was selectively breeding naturally low-emitting animals, and research so far had not found any evidence that this would come with production penalties for farmers.
Another goal was the development of a vaccine, or antibiotic-type inhibitors, that knocked out or suppressed the methane-making microbes in the cow's rumen.
Scientists were also looking at how animal feeds could be improved.