What is MUN?
MUN stands for Milk Urea Nitrogen, and it is a value that indicates the quantity of urea excreted in the milk of a dairy cow. Urea can also be released from the cow via urine and saliva. The standard unit for MUN is mg/dl. Regarding MUN levels, 10-14 mg/dl is a good benchmark for a milk sample, though acceptable levels may vary between breeds.
How is MUN Produced?
MUN is produced when rumen microbes are unable to convert rumen-degradable protein into microbial protein. Instead of becoming microbial protein, excess nitrogen found in protein sources is converted into ammonia. This ammonia is absorbed into the bloodstream, where it is redeposited in the liver and converted to urea. From there, the urea is passed on via the bloodstream to the urine and milk.
Low MUN Levels
Low MUN levels, less than 10 mg/dl, are common when feed sources lack protein or when protein in the total diet is improperly balanced. Below-average MUN levels typically indicate that rumen microbes do not have sufficient levels of rumen-degradable protein to function optimally. This often results in reduced production and potentially decreased milk protein in the sample. Low MUN levels can be corrected by adding a good quality source of rumen-degradable protein in the correct quantity to balance the total dietary protein. Adding urea to the diet, as recommended by a nutritionist or technical advisor, can also help elevate MUN levels.
Average MUN levels
Average MUN levels, in the ideal range of 10-14 mg/dl, are what one should aim for in a milk sample analysis. This indicates that the diet is well-balanced and that no energy is wasted or underutilized in the process of milk production. At these levels, a dairy cow is performing efficiently.
High MUN levels
High MUN levels, typically starting at 16 mg/dl and above, indicate an excess of protein in the diet that the cow is not fully utilizing. This often occurs in spring, when the grass is lush and contains high amounts of rumen-degradable protein. While the cow can convert some of these soluble proteins into bypass proteins for milk production via microbes, it cannot convert all the rumen-degradable proteins.
There are several potential causes for high MUN levels. One is simply an excess of rumen-degradable protein. Another reason could be insufficient energy to help break down the protein. High MUN levels can also occur when too much NPN (Non-Protein Nitrogen) is fed, which can suggest overfeeding urea.
To correct high MUN levels, various feeding factors can be adjusted. Ensuring that the ratio between energy and protein in the diet is balanced is essential. Assessing the types of protein sources used in the diet may help determine the cause. Removing unnecessary additives, such as urea, at this time can also help lower MUN levels.
During spring, grass quality can present a challenge, as it naturally contains higher amounts of rumen- degradable protein. In such cases, a De Heus technical advisor can suggest an additive designed to convert excess rumen-degradable protein into protein available for milk production.
Ending Thoughts
MUN management is often overlooked, but when managed effectively, it can positively impact not only milk production but also the overall health of a dairy cow by ensuring energy is used efficiently.
If MUN levels and the overall health of your dairy cows are a concern, contact a local De Heus technical advisor can provide tailored insights and solutions - https://www.deheus.co.za/meet-our- team/.
