A new Canadian-led study, testing the math used to estimate the greenhouse gas (GHG) output from belching, farting dairy cows, shows the current models either overshoot or undershoot the mark.
The equations used to predict cows’ methane emissions are inaccurate and need improvement soon to help dairy farmers adjust their animals’ GHG releases, according to the study co-authored by scientists from the University of Guelph, the University of Manitoba and Wageningen University in the Netherlands.
New models are needed soon, as delegates meet in Mexico this month to discuss a successor to the Kyoto accord on climate change and “scientists and policy-makers continue to debate the causes of climate change, including the level of emissions from livestock and fossil fuels,” the researchers said in a Guelph release.
The study, published this month in the journalGlobal Change Biology,looked at data from previous work in Canada, the Netherlands and the U.K. to see how well widely used equations have predicted methane production.
Then the team compiled a dataset of “actual observations” on methane emissions of dairy cattle, based mostly from respiration chamber experiments, in which methane produced in the gut of the cow is accurately determined.
These observations were then used to evaluate the “predictive power” of equations to estimate methane production.
And nine of the equations used in whole-farm greenhouse gas models either over-or underestimate cows’ methane emissions, the new study found.
The 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, said the study’s lead author, Guelph PhD student Jennifer Ellis.
In fact, the study found, most of the equations now used don’t involve any dietary data at all, but estimate methane production based on feed intake or milk output.