Use of Milk Urea Nitrogen in Herd Management

Milk urea nitrogen (MUN) has been proposed as a management tool for nutritionists and dairy farmers to use as a monitor for protein feeding rates and nitrogen metabolism in lactating dairy cows. Dietary crude protein (CP) content has the greatest nutritional influence on MUN concentrations and has the potential to be used as a management tool for assessing dietary protein feeding. The MUN concentrations are also influenced by a number of other nutritional, cow, and environmental factors. Several statistical analyses of DHI data bases report mean MUN concentrations for Holstein cows ranged between 12.7 to 15.5 mg/dL and 14.1 to 14.4 mg/dL for Jersey cows. A number of milk marketing organizations test every farm’s bulk milk samples for MUN, and DHI organizations can test individual cow milk samples for MUN. Before reformulating a diet, the nutritionist and herd manager should investigate and consider all possible reasons why MUN concentrations are above or below what they regard as desirable for the herd or cow group. Basing diet reformulation solely on bulk tank or individual cow MUN concentrations may be too hasty and unwise. The purpose of this paper is to discuss the role that monitoring MUN can have on herd management.