Trials carried out by New Zealand scientists have shown that changing pastures can directly reduce the emissions of methane - a potent greenhouse gas - from sheep and cattle. The researchers say it all depends on tannins, which are the yellow-brown chemicals found in many plants.
Scientists at New Zealand's agricultural research institute, AgResearch Grasslands, tested the legume lotus and found that its natural condensed tannin compounds reduced the methane emissions from ruminant animals by as much as 16%.
The role of plants with condensed tannins in lowering methane emissions has been known for some time, says Dr. Julian Lee, of AgResearch Grasslands. "For a given amount of dry matter intake by a ruminant, as the nutritive value of the plants increases the amount of methane emitted per unit of productivity decreases. So, while productivity goes up, methane in relation to productivity as a proportion goes down," he says.
Lowering New Zealand's methane emissions is necessary if the country is to meet its targets under the Kyoto Protocol, the international treaty that aims to reduce human influence on the global climate. As a byproduct of their digestion, New Zealand's 45 million sheep and eight million or so cattle produce about 90% of the country's methane emissions. In total, they are responsible for an estimated 43% of all the country's greenhouse gases.
The average New Zealand dairy cow produces almost 200 pounds of methane per year, equivalent in energy to 40 gallons of gasoline.
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