Methane Reduction Research
Methane reduction research takes another tack by targeting food supply to the rumen.
Methane is a potent greenhouse gas (GHG) and ruminants are a significant source, equating to about 16% of New Zealand’s agricultural GHG emissions. This international study seeks ways of reducing rumen methane production by identifying organisms that produce hydrogen (H2) and methyl (CH3) compounds, and finding ways of reducing the supply of them to methane-producing (methanogenic) bacteria.
Methane (CH4) is an important GHG with a global warming potential 25 times greater than carbon dioxide (CO2). CH4 accounts for about 14% of total global GHG emissions and about 40% of this comes from agriculture, with the single largest source being ruminant animals (cattle, sheep, deer, goats).
In New Zealand, agriculture accounts for about 48% of all GHG emissions, and CH4 from our cattle, sheep, goats and deer account for around a third of that. However, our ruminants are also important economically as sources of meat, milk and fibre, and worldwide demand for these products is predicted to double by 2050. So we need to find ways to reduce ruminant methane emissions while still producing these products for local consumption and export.
CH4 is produced when plant material is broken down by rumen microbes into compounds that can be used by the animal for growth and production of foods and fibres. This fermentation process generates waste products that can’t be used by the animal and so must be removed, otherwise they stop the fermentation. Removal is done by methanogens that convert the waste products into methane gas, which is burped into the atmosphere.
Methanogens make CH4 either by using hydrogen H2 to reduce CO2 to CH4 or by using H2 to reduce methyl CH3 compounds to CH4. Consequently CH4 mitigation research targets these bacteria, and several large programmes developing anti-methanogen vaccines or small inhibitory compounds are well advanced. Other programmes breeding for low CH4-emitting animals, or screening for forages that result in low CH4 emissions, are also underway.
This programme takes a different tack, says project leader Graeme Attwood. “Instead of directly targeting the methanogens, we are targeting the supply of food those organisms use in the rumen, and that's mainly hydrogen and methyl compounds,” he says. “So we are looking at the organisms in the rumen that make those compounds and trying to find ways of controlling their production, and hence reducing methane formation by the methanogens.”
Dr Attwood is principal scientist with AgResearch based in Palmerston North. The project involves collaborations with Otago University, Hokkaido University, Japan and the University of Illinois, USA. It is a Global Programme in Livestock Emissions Research (GPLER4) programme, which strongly encourages international collaboration.
Researchers in the project have screened massive amounts of DNA sequence data from the rumen microbiomes (the varied microbial population) of sheep selected for low or high CH4 emissions. This has led to the discovery that in low CH4-emitting sheep, several non-methanogenic bacteria thrive and compete effectively with methanogens for H2. Another finding was that competition induced one significant bacterium to change its metabolism and produce less of the precursors of methane.
Graeme Attwood says that these findings support their strategies of mitigating methane emissions by supporting and validating the selection of low CH4-emitting animals, and through changing microbe activity by developing dietary supplements and inhibitors of CH4 formation.
Fourteen inhibitory compounds have been tested on five key species of H2 and CH3 producing bacteria, and six have been shown in in vitro assays to be effective in reducing methane formation.
Detailed findings will guide the next phase of research, which will hopefully lead to specific feed additives or other strategies for on-farm methane reduction.
Showdown Productions Ltd. Rural Delivery Series 16 2021