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 atio 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.
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.
Contact your Minnesota DHIA Field Representative or the Minnesota DHIA state office about starting your herd on a regular MUN testing program.
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.
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.
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.
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 12-18 mg/dl. Levels above 18 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 12 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.
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.
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.
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.
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.
Average or "normal" MUN values are somewhere between 14 and 15 mg/dl with some producers preferring 16 to 17 for high producing cows. Values in excess of 18 or 19 would be considered high and may indicate over feeding of protein or underfeeding carbohydrates. MUN values below 12 may indicate protein rations could be increased to increase milk production without stressing the cows.
The standard deviation is also provided for each lactation group. The higher the standard deviation, the greater the spread in the MUN values for that group. For example, if the average were 14.5 with a standard deviation of 2.0, it means that
66.7% of the cows are within plus or minus 2.0 of the average, or
66.7% of the cows are between 12.5 and 16.5.
This would be considered a somewhat tightly bunched group of cows. If the standard deviation were 4.0, it would mean that the values are more widely scattered with 66.7% of the cows between 10.5 and 18.5.
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.
The MUN plots visually display the distribution of MUN values in graph form with MUN values on the vertical axis and days in milk on the horizontal axis. Individual cows are plotted on the chart by their lactation number. Individual cows on the plot can be identified by referring to the MUN report and locating the corresponding lactation, days in milk and MUN value. Dairy Comp 305 owners can use the cross-hairs function to locate the cow on the screen and press F2 to display the cowcard for that animal.
A simple method of analyzing the plot is to draw three horizontal lines across the plot. The first line should be at your goal MUN value, of say, 14.5. Draw a second horizontal line at the top of the acceptable MUN range at about 16, and a third line at the bottom of the acceptable range about 12. By counting the number of cows in the acceptable range and dividing by the total animals tested you will be able to calculate the percentage of your cows in the acceptable range (75% or above would be desirable.) The next step would be to evaluate the cows outside the acceptable range. Cows below the acceptable range could benefit from increased protein in the ration and cows above the acceptable range could have their protein ration reduced or carbohydrate levels increased to bring the MUN levels down to an acceptable level. Remember that a minor change of 1 - 2 points in MUN levels from month to month are normal and do not in themselves reveal a change in the ration or animal health. This is why establishing baselines are so critical to future herd management decisions.
Additional lines can be drawn using different colored pens at the averages of each of the lactation groups for comparison between groups. Your field rep, veterinarian, or feed consultant can also print you additional copies of the MUN plots by individual lactation group, so you can evaluate them separately. Contact your field rep or the state office for further assistance on these optional reports.
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.
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.