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.Keywords: Milk urea nitrogen, environmental factors, dairy herd management
Highlights
The Holstein breed is one of four major South African dairy breeds that undergo routine genetic evaluation by the Agricultural Research Council’s (ARC) Animal Production Institute (Mostert, 2007; SA Yearbook, 2009/10)
The overall mean for milk urea nitrogen (MUN) in the current study was within the standard range (8 - 25 mg/dL) for cows participating in the South African National Dairy Animal Recording and Improvement Scheme
Factors that had a significant effect (P
Summary
In the 2010 test year, 29 004 registered and 26 571 commercial Holstein cows participated in performance testing in South Africa. This accounted for 41% and 48% of the registered and commercial cows in the national herd, respectively (NMRIS, 2010). The concentration of urea in milk, commonly known as milk urea nitrogen (MUN), is an important tool in dairy herd management. The result would be a reduction of environmental nitrogen pollution through dietary manipulation and overall management adjustments (Schepers & Meijer, 1998; Jonker et al, 2002a)
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