Monitoring Diet Changes with MUN

MUN is another component (like protein and butter fat) that can be measured in milk. It is an important measurement because it indicates how effectively the cow is using the protein in her diet. MUN values that are higher than the recommended range generally mean the cows have too much protein in the diet or that there is an imbalance between the protein and energy. This means the cows are not using their feed as effectively as possible. MUN values below the recommended range suggest the animals are not getting enough protein in the diet and could be sacrificing production.

Dairy One deploys an “alert” system for Milk Urea Nitrogen testing on all herds in our DHI testing programs. The system analyzes the herd, pen, lactation group, and lactation stage to identify MUN that is out of range for any of those groups. We consider MUN  in the range of 8-14 to be relatively normal with no drastic need for attention. The alert is triggered when less than 50% of the herd is not in that 8-14 or “okay” range. When an alert is signaled the DHI technician who tested the herd receives an email with an attached specialized MUN report for them to communicate to the farm or farm advisor with permission of the farm.

During the past month we have noticed that herds generating an alert appear to have an increased percentage of the cows in the herd, pen, lactation group, or lactation stage out of the expected “okay” range of 8-14. There are a number of reasons that this may be occurring. While not all of these reasons may be costly, some could have detrimental long term effects on the herd. It is up to the farmer and any advisors they work with to determine what action is needed.

Some causes for MUN levels outside of the “okay” range are as follows:

  • Seasonal change in forage consumption like less corn silage, increased hay crop silage, pasture feeding, or baleage feeding
  • Reducing corn grain or other carbohydrate sources in the diet
  • Changes in TMR particle sizing and/or moisture levels
  • Feeding management that enhances feed sorting
  • Lack of forage testing to properly balance a diet
  • Inadequate or excessive amounts of ruminally degradable protein (RDP) in the diet
  • Protein content of diet lower than expected
  • Poor delivery of feed and insufficient carbohydrates present at the optimal time in the rumen

The first report is a larger herd where most of the herd has MUN well within the target of 8-14. We see however that all fresh cow pens and lactation groups show not only a high average MUN but 80+% of those cows above a 14 and as high as 24.

The second report is from a smaller colored breed herd. While we might expect slighter higher MUN for a high components breed we should be concerned about the extreme spread from low to high MUN cows as well as the fact that 80+% of the herd is above 14.

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