Pastures show way to cut gas

Agricultural scientists say pasture trials being carried out at Palmerston North may offer farmers, and the Government, a way to lower methane emissions from livestock.

The Government last week proposed a "carbon tax" to meet its obligations under the Kyoto Protocol to reduce emissions of greenhouse gases - but said it would exempt farmers from tax on methane emissions from belching livestock.

Because farmers had no way to reduce methane from deer, sheep and cattle, they would be expected to help to finance research on cutting methane and nitrous oxide emissions, at a level equivalent to 20c a sheep.

But AgResearch scientists Garry Waghorn and Michael Tavendale said grasslands scientists already working on the problem had proven for the first time that condensed tannins found in some pasture species could reduce methane emissions by as much as 16 per cent.

Tavendale said the finding had big implications for the Government's greenhouse gas management, because methane was the most significant of the gases New Zealand had to reduce.

Methane makes up about 55 per cent of the country's greenhouse gases, and about 90 per cent of the total methane emissions come from livestock.

Methane is belched up by sheep and cattle as a byproduct of the fermentation of fodder in the rumen.

AgResearch has for some time been evaluating grasses, legumes and silages fed to cows and sheep to understand their contribution to methane production.

But it also leads a national methane research consortium including people in the meat, wool, dairy and deer sectors, as well as Wrightson, a private-sector seed merchant.

Wrightson was recently knocked back by the Government's Foundation for Research Science and Technology on its separate research proposal to use $1 million in public funds to investigate the relationship between livestock digestion and the production of greenhouse gases.

But it is also spending $500,000 on developing seed lines for pasture likely to produce less methane when digested by livestock.

Pathways to reducing methane emissions include cutting animals' energy losses in the form of methane, and identifying the microbes producing methane in the gut.

One method could be to use animal feeds with naturally higher levels of condensed tannins, such as the pasture legume lotus, or to alter pasture plants to have higher levels of the most useful condensed tannins.

Or scientists could make ruminant digestion more efficient by adding supplements to the feed, or by spraying bacteria which would aid efficient digestion onto pasture.

Either way, farmers would get cattle that produce more beef or more milk or sheep that produce more wool for the same amount of food, as well as reducing the methane emissions.

This could have global benefits.

Another method might be to find breeding lines of cattle or sheep that naturally have lower methane emissions, and are more efficient food converters.

Work done by dairy researchers at Dexcel in Hamilton, has shown digestion of forage species such as lotus produce less methane than common New Zealand grasses.

But the AgResearch work was thought to be the first animal study to clearly show that dietary condensed tannins reduced ruminant methane emissions.

Besides reducing methane emissions, condensed tannins improve milk yields, increase liveweight gain, decrease internal parasites and reduce bloat, dags and fly strike.

- NZPA

nzherald.co.nz/climate

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