Abstract:
By knowing the milk urea nitrogen (MUN) content of dairy cows, the efficiency of dietary nitrogen
utilization can be improved. The main objectives of this study were to identify and quantify environmental
factors affecting MUN in South African Holstein cows. This will enable better interpretation of MUN results
by accounting for such factors. A total of 82 900 test-day records of 9 901 Holstein cows from 40 herds
participating in the South African National Milk Recording and Improvement Scheme (NMRIS) during the
period 2007 to 2010 were used. An analysis of variance was performed to determine environmental factors
significantly affecting MUN. Significant factors were herd-test-day, year of calving, parity, number of times
milked per day and lactation stage. Herd-test-day had the largest effect, accounting for 48.3% of the total
variation. Trends in least squares (LS) means for MUN over lactation stages were similar for all parities;
however, means were slightly lower in parity 3 than the first two parities. The LS mean for 2008 was the
lowest (13.9 mg/dL) in comparison to other years. Cows milked twice daily had a higher MUN LS mean
(15.5 mg/dL) in comparison to those milked three times per day (13.4 mg/dL). Results of this study provided
the basis for proper use and better interpretation of MUN data.
