Feed Management Practices That Limit Overfeeding Of Protein Can Be Evaluated By Monitoring MUN Levels

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Feed Management Practices That Limit Overfeeding Of Protein Can Be Evaluated By Monitoring MUN Levels

Dairy Pipeline: July 2007

Charlie Stallings
Extension Dairy Scientist, Nutrition & Forage Quality
(540) 231-3066; cstallin@vt.edu

Milk urea nitrogen (MUN) is a direct indicator of protein status of animals and can be used to predict over or under feeding. Factors that can influence MUN concentrations are: rumen degradable and undegradable protein intake, energy intake especially rumen available energy needed to capture rumen available N, heat damage resulting in reduced protein and energy digestibility, consumption of water because dehydration increases MUN, and feed sorting. Best management practices to prevent overfeeding of protein are:

Balance ration for total protein, rumen degradable and undegradable protein, and rumen available energy as measured by nonfiber carbohydrates or starch as well as total energy
Monitor dry matter intakes weekly on all groups and calculate N intakes relative to requirements
Analyze feeds monthly for total protein, plus heat damaged protein (more than 10% of protein in the fibrous fraction (ADIN or ADFCP )) in feeds if excessive heating is suspected
Group cows by production, feed accordingly
Prevent feed sorting by feeding a ration properly mixed with uniformity of feed delivered; particle size separation at different feed bunk locations can be monitored by use of a particle size separator
If bulk tank MUN is above 14 mg/dl, consider modifying the ration; rations below 12 are considered best from an environmental standpoint
If bulk tank MUN is below 10 mg/dl, protein consumption may be low or feeds may be heat damaged

Dr. Rich Kohn from the University of Maryland has lead a project working with milk cooperative labs reporting MUN’s in our region. Lab methods have been standardized resulting in uniform reporting. In other words, results from one lab should be comparable to another. Virginia Tech and Virginia Cooperative Extension are cooperating with this project and can supply technical support to herds that have abnormal levels. More information will be available in written format and on our web site (www.vtdairy.dasc.vt.edu).

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