TOKYO (Reuters) - The cast offs from snacking on cashews may help fight global warming caused by animals that belch methane.

Tests in Japan have show that oil produced from the shell of the cashew nut may slash by 90 percent the methane emissions from belching cattle when mixed as an additive to feed, a spokesman for oil refiner Idemitsu Kosan Co said on Wednesday.

The firm's research division is working with Hokkaido University on Japan's northernmost island, on the project, with the aim of launching sales within four years, the spokesman said.

"We are in the process of applying for a patent," he said, although the research has so far been only in the laboratory with the treatment yet to be fed to cattle.

Methane emissions from livestock in the field are a major factor in climate change.

In New Zealand the two main gases from agriculture, methane from livestock and nitrous oxide from fertilizers, make up close to half of the country's emissions.

The oil would add a few yen (cents) per day in cost per animal, the spokesman said.