MILK UREA NITROGEN ANALYSIS
Ronald L. Boman
USU Extension Dairy Nutritionist

Rocky Mountain DHIA will soon be able to determine Milk Urea Nitrogen (MUN) values for a nominal fee along with the usual protein, fat, and somatic cell values. As a nutrition and management specialist, I'm excited about what this extra analysis can do to improve the bottom line for dairy producers and also reduce the potential for nitrate contamination of our surface and ground water.

Urea is produced in the liver from ammonia derived mainly from the breakdown of feed in the rumen. Excess rumen degradable protein or too much total dietary protein in relation to rumen fermentable energy are the main causes for elevated urea nitrogen levels in blood, milk, and body tissues.

Urea nitrogen levels in blood plasma, blood serum and milk of an individual cow are essentially the same. Therefore MUN values are representative of urea nitrogen levels of blood and other body fluids. Group averages of 12 to 16 milligrams (mg) of urea nitrogen per 1/10 liter (100 ml) are considered normal. Lower than 12 mg usually indicates a dietary protein deficiency. Higher than 16 mg is due to excess dietary protein or an imbalance of ruminal protein and energy, and is associated with reduced milk yield, lower true protein content of milk and reduced feed efficiency (it requires extra energy to convert ammonia to urea). MUN values higher than 19 or 20 mg/100 ml are associated with impaired reproductive performance.

Monthly individual cow MUN values allow you, your nutritionist and/or veterinarian to make the necessary ration and management changes to optimize milk production and reproductive performance.

Monthly individual cow test day MUN values determined right along with the protein, fat and somatic cells is the way to go. The DHIA sample is more representative of the daily milk production than stripping before or after milking and gives the most reliable MUN value. This allows you, your nutritionist and/or your veterinarian to monitor ration protein and energy relationships and to optimize your feeding and ration management programs.

Excess dietary protein, protein quality imbalances, and too much protein in relation to dietary energy are not only unnecessarily expensive, but they also cause metabolic, physiological and environmental problems.

In conclusion, monthly MUN values on all cows in your herd can help us reduce feed costs, improve milk yield, improve reproductive efficiency, reduce the potential for environmental contamination and put more money in your pocket.

For additional information contact your extension agent, nutritionist, or veterinarian. ©