clipped from: www.nytimes.com 
Some of the 75 dairy cows at Guy Choiniere’s farm in Highgate, Vt., where feed has been changed to plants like alfalfa and flaxseed to reduce the methane emitted when they belch.
Guy Choiniere, part of the Stonyfield Farm experiment, has seen methane drop by 18 percent.
HIGHGATE, Vt. — Chewing her cud on a recent sunny morning, Libby, a 1,400-pound Holstein, paused to do her part in the battle against global warming, emitting a fragrant burp.
Libby, age 6, and the 74 other dairy cows on Guy Choiniere’s farm here are at the heart of an experiment to determine whether a change in diet will help them belch less methane, a potent heat-trapping gas that has been linked to climate change.
Since January, cows at 15 farms across Vermont have had their grain feed adjusted to include more plants like alfalfa and flaxseed — substances that, unlike corn or soy, mimic the spring grasses that the animals evolved long ago to eat.