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The language of nutrition: MUN

Jessica Tekippe for Progressive Dairyman Published on 05 August 2016

In laymen’s terms, what does MUN stand for?

MUN stands for milk urea nitrogen and is commonly found on every farmer’s bulk tank readings. MUNs of 5 or lower should be of concern, as the protein being fed may not be enough to meet the needs of rumen bacteria.

MUNs between 7 and 12 are very satisfactory and probably represent a good range for meeting the protein needs of the rumen bacteria and cow.

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What is its significance to the ration?

MUN levels that are too high or too low can steal from a dairy’s profits. Overfeeding or underfeeding protein, or feeding a ration with an unbalanced protein-to-carbohydrate ratio, can decrease feed efficiency, increase feed costs and lower milk production. MUN analysis can be used to identify potential problems in a feeding program.

How is MUN measured?

MUN levels are measured in milligrams per deciliter. Measurements of MUN levels can be made using reagents that react with ammonia and are read with spectrophotometers, dipstick urease pH methods or infrared technology. Many dairy processors report the herd’s bulk tank MUN.

They test the sample pulled for component, antibiotic and somatic cell count testing. Herds enrolled in individual cow sampling programs will often be given results from the sample pulled by the tester.

What impact does MUN have on a ration?

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 milk production. Most of this nitrogen comes from feed. When a cow eats too much protein, she excretes the excess nitrogen in her milk and urine.

Underfeeding and overfeeding are not the only things that MUN can help monitor. Other uses for the milk test include monitoring the impact of heat abatement procedures, predicting acidosis and revealing when cows are using more energy than they are consuming early in their lactations.

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Insufficient rumen-degradable carbohydrates may also be a factor with high MUNs, but this is less likely than cows being fed excess or highly degradable protein.

What contributes to elevated MUN?

With dairy cows, elevated MUN levels typically result from one of two likely causes. First is the rumen degradation of protein, and the second is degradation of protein by tissues.

Digestion of protein in the rumen releases ammonia that can be utilized by rumen bacteria. Excess ammonia, absorbed in the rumen, must be converted into urea by the liver for detoxification.

Ammonia is produced by the breakdown of protein during tissue metabolism and is very toxic. Urea is formed from ammonia in the kidneys and liver. Urea, a small organic molecule composed of carbon, nitrogen, oxygen and hydrogen, is a common constituent of blood and other body fluids.  PD

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