MILK UREA NITROGEN (MUN) TESTING

MUN TESTING AND PROFITABILITY Milk Urea Nitrogen (MUN) levels that are too high or too low can be robbing you of profits. Over feeding or under feeding protein, or feeding unbalanced protein to carbohydrate ratio rations can decrease feed efficiency, increase feed costs and lower milk production. MUN analysis can be used to identify potential problems in your feeding program.

BENEFITS OF MUN TESTING:

   According to Mike Hutjens of the University of Illinois, as quoted in Agriview, looking at the amount of urea nitrogen in a cow’s milk can provide an accurate reflection of how much nitrogen that cow is absorbing but not using for growth or to make milk.  Most of this nitrogen comes from feed.  When a cow eats too much protein, she excretes the excess nitrogen in her milk and her urine.

 

   Testing individual cows and whole herds can establish a baseline MUN level.  From there increases or reductions in MUN can be tracked and analyzed.  Hutjens advised looking for answers if MUN drops or rises more than two or three points from the baseline.

 

   Underfeeding and overfeeding are not the only things that MUN can help monitor.  Hutjens sees other uses for the milk test, including the monitoring the impact of heat abatement procedures, as a predictor of acidosis, and can reveal cows that are using more energy than they are consuming early in their lactations.

 

   Jim Linn of the University of Minnesota says MUN has value in evaluation of protein and carbohydrate feeding to dairy cows. MUN values in the mid-teens and higher are probably too high today.  Either the total protein in the ration or the type of protein (rumen degradable) is higher than necessary when values are mid-teens and above.

 

   Insufficient rumen degradable carbohydrate may also be a factor with high MUNs, but less likely than feeding excess or highly degradable protein.

 

   MUNs of 5 or lower should be of concern as we may not be feeding enough protein to meet rumen bacteria needs.

 

   Thus, MUNS between 7 and 12 are very satisfactory and probably a good range to meet protein needs of the cow and rumen bacteria.  

 

10:1 RETURN ON MUN TESTING!

 

Cornell University research has indicated a 10-1 return on the cost of MUN testing. This reflects potential savings in feed costs and reduced days open if MUN testing leads to a reduction in MUN as a result of feeding program changes.

 

At 15 cents per sample, the investment in DHIA MUN testing can pay for itself pretty fast.  At $15 for a 100 cow herd, it doesn’t take long for a return on that investment given the price of protein these days.  It is useful to group cows by lactation number, days in milk, or milk, and there should be at least 10 cows in a group to create a true group MUN value.

 

Contact your Minnesota DHIA Field Representative or state office staff about starting your herd on a regular MUN testing program.

 

MILK UREA NITROGEN BASICS
WHAT IS MILK UREA NITROGEN (MUN)?

Urea is a small organic molecule composed of carbon, nitrogen, oxygen, and hydrogen. Urea is a common constituent of blood and other body fluids. Urea is formed from ammonia in the kidneys and liver. Ammonia is produced by the breakdown of protein during tissue metabolism and is very toxic. Digestion of protein in the rumen releases ammonia that can be utilized by rumen bacteria. Excess ammonia absorbed by the rumen must be converted into urea by the liver for detoxification. Thus, in dairy cows there are two entry points which may elevate blood urea (BUN), the first is rumen degradation of protein, and the second is degradation of protein by tissues. The capture of ammonia in the rumen will be influenced by grain intake, which improves rumen microbial growth. Therefore, digestion of protein and carbohydrates in the rumen will influence BUN concentrations and tissue metabolism of energy and protein.

Increasing the amount of energy absorbed from digestive processes will spare protein catabolism and result in lower blood urea levels. Urea however is non-toxic and can be at very high levels without causing any problems. If the kidneys and liver did not convert ammonia into urea, animals would get very ill every time they ate. The conversion of ammonia into urea in the liver prevents ammonia toxicity. Urea is then excreted from the body in urine. Urea diffuses readily into body tissue, blood and milk. Urea is a normal part of the non-protein nitrogen found in milk.

Many scientists agree that Blood Urea Nitrogen (BUN) and MUN values are equivalent if the sample has been collected, handled and analyzed properly. Urea is thought to diffuse into, and out of, the mammary gland so urea in the milk equilibrates with blood urea very quickly.

HOW IS MUN MEASURED?

MUN and BUN concentrations fluctuate during the day and vary with food and water intake, milking time, environmental conditions, stress and time of day. Concentrations will be highest about 4 to 6 hours post feeding. Therefore, it is important to take milk samples at normal milking time, and at the same time each test, always being aware of the causes of MUN level fluctuations. MUN is measured using the same milk samples that are taken on test day. MUN levels are measured in milligrams per deciliter (mg/dl). Blood Urea Nitrogen testing can be used but is unpopular because it requires the drawing of blood for analysis. Measurements of milk can be made using reagents that react with ammonia and are read with spectrophotometers, dipstick urease pH methods, or infrared technology.

WHEN SHOULD I TEST FOR MUN?

Ideally every month, but you can monitor your herd by testing for MUN as little as every three to four months or whenever feed rations or methods of feeding change. Examples of significant feed changes include: nutrient concentration changes of more than 1%, when feed ingredients or ingredient ratios change, when cows are turned out to pasture, or if the particle size or moisture levels change. All of these changes can influence protein efficiency.

WHERE DO I START WITH MUN TESTING?

Jim Linn, University of Minnesota Dairy Science Specialist, recommends a minimum of six months of MUN tests to establish a baseline. Baselines can then be used to set goals for each individual herd. Those goals can then be used to make herd management decisions. Given the constraints of available feed and other environmental conditions, it may not be possible to reach a particular MUN value, but it will allow you to measure progress toward a particular goal.

WHAT SHOULD MY MUN VALUES BE?

MUN concentrations vary from herd to herd and within cows of the same herd. The mean urea concentration of Holstein cows tested in Pennsylvania was 14.3 mg/dl with a standard deviation of 4.2, meaning 66.6% of the cows were between 10.1 and 18.5 mg/dl, and 95% of the cows were from 6-20 mg/dl. These are average values and not optimum feed utilization levels.

Obviously, there is a wide variation in MUN levels between cows. Given the variation in MUN, values for individual cows should not be interpreted. They are not to be used to move cows from one group to another but should be used to calculate a mean value for groups of at least 8 cows. Typically, the range should be between 7-12 mg/dl. Levels above 12 indicate crude protein levels may be too high, rumen fermentable NFC may be too low, or protein and NFC may not be properly combined in the diet. A low MUN value under 7 indicates low crude protein in the rations, improper mix of undegradable and degradable protein, and/or high rumen fermentable carbohydrates (NFC).

The range of MUN concentration for individual cows consuming the same diet is +6 to -6 from the mean of the group. That is, if a group of cows averaged 12 MUN mg/dl, 95% of the group would fall between 6 - 18 mg/dl. High producing cows will generally have higher MUN levels due to the increased feed rations needed to maximize milk production.

IF MUN LEVELS ARE ABOVE 12 mg/dl, SHOULD I TRY TO REDUCE THEM?

Higher levels of MUN concentration suggests there are opportunities to improve your protein feeding system. Just what needs to be done should be decided with your nutritionist. High MUN values indicate crude protein levels are too high, rumen fermentable non-fiber carbohydrates (NFC) is too low or the ratio of protein and NFC are not properly balanced.

WHAT IF MY MUN LEVELS ARE BELOW 7?

Low crude protein is easy to correct and is often a simple matter of supplying more rumen degradable protein. A low MUN can be associated with decreases in milk and milk protein.

WILL MUN TESTING SOLVE ALL MY NUTRITION PROBLEMS?

No, Milk urea testing is a useful diagnostic tool to identify opportunities to improve protein supply. If your MUN value is between 10-14, your protein is most likely adequate. However, a word of caution, milk urea may be within acceptable ranges of 10-14 but protein may still not be adequately balanced. Additionally, milk urea should never be interpreted without evaluating overall feeding management programs. Milk urea is a useful tool but should not be used in isolation from evaluating other management procedures involving production and nutritional efficiency within the herd.

HOW DO I INTERPRET MUN RESULTS?

The Minnesota DHIA MUN report lists the cows by barn name with DIM, lactation, milk weight, fat %, protein %, SCC and MUN values for each cow tested. A summary report is also produced that provides averages by stage of lactation and by lactation groups 1, 2 and 3 or greater. These reports are also available through Scout and Dairy Comp 305 and can be sorted by MUN value in ascending or descending order.

Cows with very low MUN values such as 1 or 2 or above 30 are most likely the result of sampling errors or spoiled samples.

Sample MUN Report                                           Sample MUN Summary

CAN SAMPLING TECHNIQUE ALTER MUN VALUES?

Yes, MUN tends to be highest in first milk and lowest at the end of milking so it is critical that the sample be mixed properly before being poured into the vial. The preferred method is to pour the sample from the first meter tube into a second tube and then back to the first tube. Swirling the sample does not adequately mix the sample and will result in higher fat and lower MUN scores if only the milk from the top of the meter is used. A properly mixed sample provides a more representative measure of the entire milking.

HOW DO I GET MUN TESTING FOR MY COWS?

The Minnesota Dairy Herd Improvement Association offers cost effective MUN testing. The reports include individual MUN scores, summaries and averages for each lactation group and a scatter plot that provides a visual interpretation of your MUN results. Users of Dairy Comp 305 and Scout can also generate various custom MUN reports and graphs on their own computers.


Questions?
Email Minnesota DHIA at admin@mndhia.org.