Cows’ GHG emissions measured inaccurately, study finds

Cows may be getting a bum rap over their greenhouse gas emissions — or not.

Mathematical equations used in predicting cows’ methane emissions are inaccurate and need improvement to help dairy farmers mitigate greenhouse gas releases, says a new study by a research team that includes scientists from the University of Guelph, the University of Manitoba and Wageningen University & Research Centre in the Netherlands.

The study appears in the November issue of the journal Global Change Biology.

Livestock accounts for about 18 percent of all greenhouse gas emissions, according to the United Nations Food and Agriculture Organization. Methane (CH4) is the most important greenhouse gas produced on dairy farms and is 25 times more potent than carbon dioxide, another important gas implicated in global warming.

These researchers used data from studies in Canada, the Netherlands and the United Kingdom to assess how well widely used equations predicted methane production. They found that nine equations used in whole-farm greenhouse gas models over- or underestimate cows’ methane emissions.

“We over- or under-predict CH4 emissions as a result of these equations,” said Dr. James France with the University of Guelph’s Department of Animal and Poultry Science. “Agriculture needs more accurate estimates based on better science.”

Jennifer Ellis, a Guelph PhD student and lead author of the new paper, notes there’s “a lot of concern right now about the impact of farming and human life in general on the environment. The prediction accuracy of these equations is small, and the equations are not suitable to quantify methane production of cows.”

Whole-farm models used to estimate the effect of on-farm management changes – such as manure and crop management, breeding, and basic nutrition – don’t account for effects of dietary changes, she said.

For example, the equation currently used by the Intergovernmental Panel on Climate Change fails to distinguish between the effects of simply feeding cows more and the effects of feeding them higher-fat diets, said Ellis, who has begun a post-doc at Wageningen University. “A higher feed intake will increase methane production. A rise in dietary fat content will decrease methane production.”