We hear a lot these days about "climate change" and "carbon footprints." Dairy nutritionists might wonder what they can do about this. Some feeding strategies involving fish oil have already been shown to reduce greenhouse-gas emissions.

Now, scientists at the USDA/Agricultural Research Service's Pasture Systems and Watershed Management Research Unit in University Park, Pa., have developed a Dairy Greenhouse Gas model, or DairyGHG, to stimulate management effects on emissions across a wide range of production systems. These include increased milk production through genetic improvement and improved feed management, increased use of forage in lactating-cow diets, and use of more corn silage and less alfalfa. A higher proportion of corn silage in the forage — relative to alfalfa — helps reduce a farm's carbon footprint in the simulation model. In fact, switching from 50 percent corn silage/35 percent alfalfa silage/15 percent hay to a forage base consisting of 75 percent corn silage/25 percent alfalfa silage reduced greenhouse-gas emissions from the whole farm by 13 percent.

"Corn silage production required less machinery and fuel compared with alfalfa, which reduced emissions from fuel combustion and secondary sources," the authors wrote in the March issue of the Journal of Dairy Science.