Short communication: Evaluation of milk urea nitrogen as a management tool to reduce ammonia emissions from dairy farms

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 14 mg/dL (prevailing industry average). For 3 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 2 freestall 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 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.