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.

As of the last reading in mid-May, the methane output of one herd had dropped 18 percent. Meanwhile, milk production has held its own.

With worldwide production of milk and beef expected to double in the next 30 years, the United Nations has called livestock one of the most serious near-term threats to the global climate. In a 2006 report that looked at the environmental impact of cows worldwide, including forest-clearing activity to create pasture land, it estimated that cows might be more dangerous to Earth’s atmosphere than trucks and cars combined.

In the United States, where average milk production per cow has more than quadrupled since the 1950s, fewer cows are needed per gallon of milk, so the total emissions of heat-trapping gas for the American dairy industry are relatively low per gallon compared with those in less industrialized countries.

[Read](http://www.nytimes.com/2009/06/05/us/05cows.html?_r=1&partner=rss&emc=rss “Read the Article”) (New York Times)