What does our milk actually cost our earth to make

Humans are the only mammals to actually drink milk not only as children but adults.  Have we really thought what goes into the making of our milk?  Urinary urea is a prime nitrogen source from dairy manure.  The study was focused primarily on changing the diet of the cows on the farms in order to see if there was less contamination of the ozone layer.  This research is interesting because the fact that we can even change the diets of cows in order to have less of an impact on the earth is incredible.  The findings were that there was a 7 to 12% decrease of NH3 and N2O in the pasture farms of Wisconsin.  The results are great because if that can be reduce with a research like this something more wide scale can certainly have a great trade off on the ozone layer while continuing to give us delicious cheese. 

                                               http://www.epa.gov/agriculture/ag101/printbeef.html

J. M. Powell,* C. A. Rotz, and M. A. Wattiaux J. Environ. Qual. 43:1169–1175 (2014).  Potential Use of Milk Urea Nitrogen to Abate Atmospheric Nitrogen Emissions from Wisconsin Dairy Farms