The global human population is projected to increase from its current estimate of 7.1 to 9.4 billion by the year 2050 (U.S. Census Bureau, 2008) . These projections are alarming since food production will have to increase between 40 and 65% (Hubert et al., 2010) and meeting such demand will be a challenge as arable land and other resources for food production are limited (Rockstrom et al., 2009; Hertel, 2011). Meeting this demand will require increased efficiency of production in all facets ofthe system. Additionally, gains in productivity cannot come at the expense of environmental health or the gains will not be sustainable. Nitrogen export to the environment can result in eutrophication of aquatic ecosystems; increased atmospheric particulates; decreased stratospheric ozone concentration; greenhouse warming; increased acidity of soil, precipitation, and surface water; coastal hypoxia; and methemoglobinemia in infants (Wolfe and Patz, 2002). The use of management tools, such as milk urea nitrogen (MUN), can help improve the efficiency of milk production, reduce feed costs, and reduce environmental problems associated with dairy production (Jonker et al., 2002b).
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