Evaluation of Milk Urea Nitrogen As a Management Tool to Reduce Ammonia Emissions From Dairy Farms.

Relationships between feed nitrogen (N) intake, milk urea N (MUN), urinary urea N (UUN) excretion and ammonia (NH₃) emissions from dairy farms were evaluated 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 emission were calculated as percent decreases in NH₃ emissions associated with a baseline MUN level of 14 mg/dL (prevailing industry average). For three studies with cows in stanchion barns, relative NH₃ emission reductions of 10.3 to 28.2% were obtained when MUN declined from 14 to 10 mg/dL. Similarly, analyses of two free-stall studies provided relative NH₃ emission reductions of 10.5 to 33.7% when MUN levels declined from 14 to 10 mg/dl. The relative reductions in NH₃ emissions from both stanchion and free-stall 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.