A scientific team identifies the rumen enzymes that control the main energy source for methane-producing microbes.
In the global quest to reduce greenhouse gases, finding ways to lower methane emissions from livestock has become a priority.
An international team of researchers led by scientists at the University of Ortago in New Zealand has identified the main rumen microbes and enzymes that control the supply of hydrogen, the main energy source for methane-producing microbes called methanogens.
Scientists at the universities of Monash in Australia, Illinois in the United States and Hokkaido in Japan collaborated on the project.
According to the report, methanogens use molecular hydrogen and other substrates to reduce carbon dioxide to methane. Given the microbes’ effect on the greenhouse gas, many programs around the world are underway to mitigate ruminant methane production.
Agriculture Canada has been researching feed strategies, additives, and feed conversion efficiencies to lower the influence of livestock feed and methane emissions.
Farmers can use Agriculture Canada’s Holos greenhouse gas calculator program, which takes a farm’s data and calculates carbon dioxide, nitrous oxide and methane emissions from rumen fermentation, manure management, cropping systems and energy use to track emissions.
But, according to research scientists, getting up to speed to modulate methanogens through dietary interventions while maintaining the health and productivity of the host animal means understanding the processes that mediate all the substrate supply to the methanogens in the rumen.
“New Zealand’s greenhouse gas emissions profile is unusual for a developed country in that around half of New Zealand’s emissions are from agriculture,” said professor Gregory Cook with the Department of Microbiology and Immunology at the University of Ortago, Dunedin. “Most of this is caused by methane emissions from enteric fermentation in farmed ruminant animals including cattle, sheep and deer, which collectively account for around two-thirds of New Zealand’s agricultural emissions.”
A lot of the work to date has focused on developing small molecule inhibitors and vaccines to target methane production by methanogens. The latest research focused on better understanding of the fermentation dynamics in the rumen and methane yields from sheep.
“The high- and low-methane yield sheep were originally selected from animals which were part of the central progeny testing flock in New Zealand, a New Zealand sheep industry supported test, which assesses rams and their progeny for a range of traits,” said Cook. “The animals were fed the same standardized diet and their methane yields were measured using respiration chambers. The sole selection was for animals representing the high- and low-methane yield extremes. These selection lines have been continued over several years to select animals with divergent methane yields.”
He said they are aware that there are differences in the rumen size and therefore in the rate of turnover of the rumen contents between high- and low-methane yield animals.
“The low-methane yield animals have a smaller rumen, and we assume their turnover of rumen contents is higher because their intakes are similar to the high-methane yield animals. We think this faster turnover leads to different fermentation dynamics in which more hydrogen is produced. When more hydrogen is produced, the concentration of hydrogen in the rumen increases, which allows hydrogen-consuming bacteria to compete with the methane-producing methanogens, which also use hydrogen but prefer to use it at low concentrations.”
The findings are important because scientists can now begin to target the supply of hydrogen to methanogens to reduce animal methane emissions. They will be able to establish strategies by controlling hydrogen supply. One strategy is to develop feed supplements that encourage non-methane producers to outcompete methanogens.
Researchers are working toward identifying specific inhibitors of the hydrogen formation process in rumen bacteria. Work will focus on screening compounds that can reduce the supply of hydrogen to methane producers without compromising animal performance and explore ways to divert hydrogen toward those microbes that do not produce methane. Cook said that the inhibitors are likely to be small molecule compounds, which could be delivered either as a supplement in feed or delivered to the rumen via slow release capsules.
“We have had positive feedback from a range of organizations with a stake in reducing methane from ruminant animals, including supportive comments from the (New Zealand) minister of agriculture, Damien O’Connor,” he said. “We are still in the discovery phase of the research program but have a defined development pipeline into which new compounds and control strategies will be funnelled to rigorously test their effectiveness in vitro, prior to testing in animals.”
Graeme Attwood, principal scientist and leader of the research program, said the discovery has opened up a new approach to reducing livestock methane emissions.
“This is vital for New Zealand to meet its greenhouse gas emission targets under the Paris Agreement and to ensure the farming of ruminants is sustainable into the future.”
Source: Glacier farmmedia
