Grain-finished beef produced 38 percent less methane, the researchers found, though other studies have reported as much as 70 percent less.
"Also, although the (total) emissions are higher on the feedlot, the animals gain weight quicker," Schulz said, so the animals are slaughtered sooner, emitting less gas overall. "On a per-kilogram-of-meat basis, the feedlot performs better," he said.
Emissions from grass-fed cows were about 20 percent higher than grain fed, according to the study, which was published in Environmental Science and Technology, and funded by Meat and Livestock Australia.
Schulz' study also concluded that raising sheep produced less greenhouse gas emissions than beef, largely because the animals have about half the lifespan of cattle.
Other studies have made the same comparison between beef from grass versus grain-fed animals and found that the higher methane emissions from grass-fed cows tip the carbon scales in favor of feedlot beef.
But some people claim that the math comes out the opposite way if carbon stored in the soil by grazing animals is incorporated: Grass-fed beef mow the pastures, fertilize the ground with their manure, and tramp around, creating healthy soil that acts as a carbon sink.