But the study also showed that Australian red meat production has one of the lowest carbon emission profiles in the world, with a carbon footprint half to a third lower than those often quoted.

The life-cycle analysis compared the greenhouse cost of producing a kilo of grass-fed beef compared to a kilo of grain-fed beef, and found that despite the emissions in producing and transporting grain, grain-feeding is more efficient from a greenhouse perspective.

It is already well known that a grain diet, which is more easily digestible than the cellulose fibres of grass and so calls on less methane-producing microbes, will in itself produce less methane.

But the life-cycle analysis by a team of researchers supported by MLA looked at all potential sources of greenhouse gas, from the fuel used in tractors and headers to the disposal of tyres and feedlot manure.

The key issue, according to the study’s authors, is that grass-fed animals take longer to reach slaughter weights, and in that time produce more methane than their shorter-lived counterparts in the feedlot.

In a comparison of two NSW supply chains, the authors found that over a lifetime a grainfed steer produced 3602 kilograms of carbon dioxide equivalents (kg CO2-e), more than the 3365 kg CO2-e a grassfed steer produced in its lifetime.

But when the analysis narrowed down to the carbon footprint per kilogram of beef, grain-finished beef came out at 9.9 kg CO2-e per kilo of beef, against 12 kg CO2-e per kilo of beef for grassfed.

However, grass-fed beef production has a range of methane-reduction options available, according to study co-author Matthias Schulz of the University of NSW.

They include using different pasture mixes and grazing management strategies, methane-inhibiting feed additives, productivity gains through management and genetics that deliver earlier-finishing animals, or the high-tech path of rumen manipulation.