Greenhouse gas emissions from livestock farms have received a lot of attention in recent years. Some studies have concluded that intensive confinement systems have the lowest greenhouse gas emissions per pound of milk or meat produced, while other studies have found that grass-based livestock farms have the lowest net greenhouse gas emissions.
Calculating greenhouse gas emissions of different farming systems is complex, and the results of each study depend on the geographic area considered and specific assumptions about management. When researchers at UW-Madison compared greenhouse gas emissions of several different dairy farming systems in Wisconsin, they found that emissions were broadly similar between grazing and confinement dairies. Most studies comparing greenhouse gas emissions of conventional and grass-based livestock systems do not examine the effect of management differences within each of those approaches. This study looked at the effect of different grain supplementation rates on emissions from grazing systems, and at the effect of adding an anaerobic manure digester on emissions from confinement dairies. The study showed that details of manure management, feeding strategies, and crop production decisions affect total greenhouse gas emissions more than whether or not a farm practices grazing.
In this model, the confinement system with the anaerobic digester resulted in the lowest overall emissions, primarily because the energy value of the methane produced in the digester reduced the need to burn fossil fuels for electricity generation. For all the other dairy farms, this model found that approaches balancing pasture intake and feed supplementation to optimize milk production resulted in the lowest greenhouse gas emissions per unit of milk produced.
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Published as Research Brief #101