We have had 166 samples or cows in which we have measured the blood concentration, the milk concentration through DHIA and also the morning and evening concentration through our own laboratory. The table contains information presenting the mean values for blood, milk urea a.m., milk urea p.m., and DHIA milk urea for 166 samples from 37 cows that were sampled repetitively from December through April in our dairy herd. Two groups are fed a high production group balanced for 90 lbs. of milk and a low production group balanced for 55 lbs. of milk. The milk urea DHIA concentration represents a composite sample taken from morning and evening samples. The milk urea a.m. and the milk urea p.m. represents samples taken on sample day and analyzed for urea concentration.
Standard deviations are very similar with the different tests.
The DHIA MUN has the highest SD 2.99 compared to 2.20 to 2.31 from milk and blood from the clinical laboratory. The range in urea values is very similar across the different tests but note, the low 2.3 on the milk urea DHIA test and the high 23.0. The range on the MUN DHIA is wider than the clinical labs. However, overall we would make similar conclusions about the MUN using any of the tests. In Conclusion Milk urea may be a useful test for diagnosing herd problems an identifying opportunities to improve protein supply.