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Measuring Urea in Milk
Dairy Pipeline: February 1998
by
Charles C. Stallings
Dairy Extension Coordinator,
and Extension Dairy Scientist, Nutrition
Virginia Tech
Measuring urea in milk has become popular as new technology allows measurement on large number of samples through DHI programs. Now milk urea (MUN) can be obtained at the same time fat, protein, and somatic cells are measured. However, equipment to do this is expensive. United DHI (serving North Carolina and Virginia) currently does not have the instrumentation to measure milk urea, but does have a system in place to send test day samples directly to Minnesota for determination of fat, protein, somatic cells, and urea. The cost of this is $.27/sample + UPS charges + $5 handling. UPS charges will vary depending on number of samples, but is somewhere around $.30 per sample. Therefore, cost of getting an MUN would be about $.70/sample, but would be offset by the $.32/sample that United DHI charges. Urea diffuses throughout the body in water. Therefore, it is in blood and milk. Also it is excreted in the urine. Urea is produced from ammonia, a toxic compound, and is a result of protein breakdown and metabolism. Consuming more protein due to increased intake or higher dietary protein concentration will result in greater blood and milk urea. Increasing energy intake will many times decrease urea due to increased efficiency of protein utilization and less protein wastage. Dehydration will result in increased blood and milk urea and increased water intake will cause a reduction. Therefore, milk urea indicates the protein, energy, and water status of the cow. Interactions of the three sometimes may make it hard to interpret results. Cows consuming the same ration will not have the same milk urea concentrations. Things such as days in milk, milk production, dry matter intake, water intake, etc. will vary from cow to cow and thus affect milk urea. Therefore, individual cow observations are hard to interpret. Group averages are more accurate and samples should be obtained from at least 8 cows or 15 to 20% of the group.