Current Progressive Dairy digital edition

0107 PD: Protein cost and MUN

Lawson Spicer Published on 10 January 2007

Are your feed costs high? The most expensive feeds are those with high levels of protein (greater than 20 percent protein). Testing for MUN (milk urea nitrogen) in the milk can help you determine the correct level of protein in the feed.

There are other reasons for testing for MUN:



•lowering feed costs

•meeting nutritional requirements

•increasing reproductive performance

•increasing milk and milk protein yield

•reducing nitrogen excretion into the environment


What is MUN? When there is more protein than the cow needs for use in her body, the excess protein is converted to urea. The urea is eliminated from the body of a lactating cow through milk, urine and feces. Milk is an easy fluid to collect. Measuring MUN level in the milk can be a simple tool for nutritional monitoring.

What is the normal range of MUN levels? The suggested range for MUN is 11 to 16 milligrams per deciliter. It is recommended to take a minimum of three bulk milk tank samples or milk string samples during testing each month to be tested for MUN. The cost for analysis is minimal and the cost ratio may be as high as ten-to-one, assuming feed changes are made.

What factors can change the MUN level?

•dry matter intake (DMI)

•water intake

•milk production


•liver function

•urinary output

•protein and energy levels

Some examples of how MUN can be used to evaluate feed and management situations are as follows. One is MUN levels quickly change (in a day or two), based on the protein level of the ration. Specifically, the MUN level can be used to monitor changes in forage lots.

For example, a dairy producer was consistently having a MUN test done each month at his DHIA test. One month the results came back higher than usual.

The only thing he did was open a new bag of haylage and use it at the same level as the previous bag. The protein content of the new haylage was much higher than the previous bag, making his MUN level go up. He made the appropriate changes in his ration, based on the analysis of the new haylage, and the MUN levels came back in line.

Research also has shown a decrease in reproductive efficiency when MUN levels are high (for example, 20 milligrams per deciliter). The effects seem to be more prevalent at 60 to 90 days in milk and slow down after that.

MUN is a valuable tool that can return far more than it costs to test milk samples. MUN can be used as a tool to monitor your nutrition program, save money, maximize production and reduce the effect of your herd on the environment. PD

Lawson Spicer