CLAIMS that cattle and sheep are responsible for 10.9 per cent of Australia's greenhouse gas emissions have been called into question after scientists discovered considerable variation in the amount of methane produced by individual animals.
Farmers, fearful of the costs greenhouse gas emissions trading will impose on their businesses, are demanding more accurate measurement of emissions before the ETS is brought in.
Beverley Henry, manager for environment, sustainability and climate change with Meat & Livestock Australia, said current estimates were based on livestock overseas, with the actual emissions likely to vary depending on diet and animal type, as well as other factors.
"At the moment, we don't reflect those in Australia's national accounts very well," Dr Henry said.
"We need to get better quantification of the emissions as well as an understanding of how much mitigation is possible."
Australia boasts 26.81 million head of beef and dairy cattle, and 69.2 million sheep, so even a small error would quickly compound in any attempt to measure the total greenhouse gas expelled by the animals.
Earlier this year, the Department of Agriculture put $11.25million into programs to reduce methane from livestock.
Cattle and sheep are ruminants. They possess a special stomach, a rumen, in which microbes ferment grass and cellulose that is otherwise indigestible. The fermentation produces methane, a greenhouse gas about 21 times more potent than carbon dioxide, which the animals burp out.
Dr Henry said scientists were looking at everything from the microbes -- how they are influenced by diet and supplements -- to the whole farm system. Already, there were improvements in efficiency. "We are now producing less methane per kilogram of beef than what was occurring in 1990," she said.
Some small-scale work five years ago revealed big differences in how much methane individual cattle produce.
Kath Donoghue, from Industry & Investment NSW, said they found roughly a 20-30 per cent difference in emissions between the high groups and the low groups. "It depended on the diet, there are a greater magnitude of difference on different diets," shesaid.
She plans to measure the emissions from more than 1000 Angus cattle, the dominant southern breed, to see if there were genetic differences in emissions.
Dr Donoghue said that while some supplements, such as cotton seed oil and palm oil, had reduced methane emissions, they were not practical in Australia's large-scale northern cattle industry.
"The thing about genetics is it is applicable in both intensive and extensive areas and it is a known technology," she said.
A lot of work would focus on the microbes in the rumen. "If we are identifying high- and low-emission animals, we can send rumen samples to the labs and they can say what is different in the rumen of these two animals and what is causing this to happen."
The CSIRO is also working on a system that will use electronic gas sensor technology "to accurately identify, develop and/or adapt a method for measuring emissions" from large numbers of animals.
An earlier study by University of Melbourne researchers found methane emissions varied from 146g an animal a day in a Victorian feedlot to 166g an animal a day in Queensland.
