The purpose of this study was to compile and evaluate relationships between feed nitrogen (N) intake, milk urea N (MUN), urinary urea N (UUN) and ammonia (NH3) emissions from dairy farms to aid policy development. Regression relationships between MUN, UUN and NH3 emissions were compiled from studies conducted in Wisconsin, California and the Netherlands. Relative reductions in NH3 emissions were calculated as percentage decreases in NH3 emissions associated with a baseline MUN level of 14mg/dL (prevailing industry average). For 3 studies with cows in stanchion barns, relative NH3 emission reductions of 10.3 to 28.2 percent were obtained when MUN declined from 14 to 10mg/dL. Similarly, analyses of 2 freestall studies provided relative NH3 emission reductions of 10.5 to 33.7 percent when MUN levels declined from 14 to 10mg/dL. The relative reductions in NH3 emissions from both stanchion and freestall barns can be associated directly with reductions in UUN excretion, which can be determined using MUN. The results of this study may help create new awareness, and perhaps eventual industry-based incentives, for management practices that enhance feed N use efficiency and reduce MUN, UUN, and NH3 emissions from dairy farms.

Source: J.M. Powell, M.A. Wattiaux, G.A. Broderick/Journal of Dairy Science