Any calculation of the carbon footprint of a gallon of milk must include fuel used by tractors and trucks, as well as electricity consumed by milking machines and refrigerators. But how much gas is coming from the cows themselves?

Researchers from Purdue University, University of California-Davis, Cornell University, the University of Minnesota and Washington State University are investigating the answer as they start a new collaborative study to measure greenhouse gases from dairy cows. The study is part of an industry-wide effort to reduce greenhouse gas emissions related to fluid milk. Carbon dioxide, methane and nitrous oxide will be monitored at five barn sites and two manure lagoons in Indiana, Wisconsin, California, Washington and New York.

Most of the previous studies on dairy greenhouse-gas emissions were done in Europe and Canada and don’t reflect U.S. climate and management practices. This study will provide country- and region-specific greenhouse-gas emission rates from U.S. dairy operations.