Milk Urea Nitrogen as a Metabolic Indicator of Protein Feeding Efficiency on Dairy Farms

Abstract

Blood urea nitrogen (BUN) is elevated in cows fed excessive levels of protein. Overfeeding protein is a major economic cost to dairy producers and elevations in BUN result in adverse health and reproductive effects. A routine monitoring system for protein feeding is needed. Milk urea nitrogen (MUN) is highly correlated with BUN. Milk is collected monthly on many farms by DHIA testing centers and milk would be easier to obtain than blood for continuous monitoring of urea concentrations. The objective of the first study was to characterize the transfer of urea from plasma in to milk following rapid IV infusion of urea into lactating dairy cows. The objective of the second study was to determine if milk urea concentration is sensitive to changes in dietary protein intake and if it would be feasible to use MUN to evaluate protein feeding on dairy farms.