Milk urea
The milk urea content in describing milk production the content of urea in milligrams per liter (mg / l) milk . Occasionally it is also given in ml / 100 ml or in ppm . The urea content helps to monitor the cow's nutritional situation. As a waste product of the amino acid metabolism, it allows conclusions to be drawn about the protein and energy supply of the animals. Depending on the feeding, the urea content is mainly determined by the amount of crude protein per animal and day, the content of flow- through protein (USD) and the carbohydrates (sugar, starch) fermentable in the rumen and thus serves as a measure for the utilization of the raw feed protein.
Since the early 1980s, testing milk for urea content to check health status and feeding has been recommended as an inexpensive method. Until after the turn of the millennium, it was only offered by some state control associations as a chargeable additional service as part of the milk performance test . In the meantime (2016) it has been one of the standard parameters examined in Germany for several years.
In the context of the fertilizer regulation is made possible "nutrient-adapted feeding" mentioned, by which a single operational higher livestock per ha with proven lower average N excretion of the stock, the analysis is the level of urea for checking the feeding.
Analytical methods
|
DIN EN ISO 14637 |
|---|---|
| Area | Food |
| title | Milk - Determination of urea content - Enzymatic method with pH change (reference method) |
| Latest edition | 2007-03 |
| ISO | 14637 |
The reference method EN ISO 14637 / IDF 195: 2004 for the determination of milk urea is an enzymatic determination with a differential pH-metric method. Urea is catalytically hydrolyzed in the reaction by urease, which produces OH¯ ions in the reaction buffer. The variation of the pH value between the start of the reaction and the end (test duration 35 seconds) is proportional to the urea concentration in the sample.
Urea + 3 H 2 O → 2 NH 4 + + CO 2 + 2 OH-
H 2 O + CO 2 → HCO 3 - + H +
Alternatively, the determination of milk urea is carried out with the help of analyzers in a continuous flow process with air-segmented sample separation. After dilution in a sodium chloride solution, the milk sample is dialyzed against a color reagent and then treated with an acid catalyst . The stream of reagents is heated to 90 degrees Celsius, whereby a color complex is formed from the urea and the color reagent in the presence of thiosemicarbazide , the absorption of which is measured photometrically . The urea content of the sample is then shown in mg per liter using appropriate software, including urea standards.
Connections
Amount of crude protein
The more crude protein the cow takes in with the feed, the higher the urea content of the milk will usually be.
Degradability of the crude protein
The higher the degradability of the crude protein, the higher the amount of nitrogen released in the rumen. However, if too much ammonia is formed in the rumen in a short time, the rumen microbes are not able to process it so quickly. More ammonia goes into the blood and is converted into urea. This is excreted in the milk. Attempts are made to counteract this problem using rumen-resistant protein (UDP).
power supply
The more crude protein a ration has in relation to the amount of energy available, the higher the milk urea content.
Ruminal nitrogen balance (rNB)
A nitrogen deficiency is possible with a ration based on corn silage. One then speaks of a negative RNB . The milk urea content is then usually low (<150 mg / 1000 ml). In the case of grazing, there is usually excess protein. The milk urea is then usually over 300 milligrams per liter. With pure pasture husbandry (full pasture) it can even reach values of 500 to 700 milligrams per liter.
Possible causes for extreme values
In principle, individual animal values should not be overinterpreted when it comes to the urea content in milk. The farmer receives a rough overview of the status of the herd from the average values of the total delivered herd milk reported several times a month by the dairy. The values reported from the individual sample of the milk control must then be viewed in connection with the protein content of the milk and should primarily be used to improve management for the entire herd.
Too high urea content (more than 300 mg per liter)
A high urea content signals an excess of degraded feed protein in relation to energy. The rumen microbes cannot convert all crude protein or ammonia to form microbial protein. The unused ammonia is converted to urea in the liver. In connection with very high protein contents, it indicates a protein and energy excess.
Urea content too low (less than 150 mg per liter)
Low urea levels indicate an insufficient protein supply. The rumen microbes can grow and multiply poorly despite an excess of energy. This is why little ammonia is converted to urea in the liver. With medium and high protein contents, a protein deficiency and energy surplus are indicated.
The better the microbial protein synthesis and the nitrogen breakdown in the rumen are coordinated, the lower the nitrogen losses in the form of urea excreted (via milk). For physiological reasons, there is no precise urea content to be aimed for for a certain milk yield. Urea levels between 150 and 300 mg per liter of milk are considered normal, with values between 200 and 250 mg per liter being aimed for.
Web links
- State control association with further information ( Memento from December 21, 2013 in the Internet Archive )
- Table of contents of DIN EN ISO 14637: 2007-03 at Beuth-Verlag
Individual evidence
- ↑ Mathias Schäfers: Investigations on the body condition assessment of dairy cows of the breed "Simmental cattle" under the housing conditions of northern Upper Bavaria , 2000, dissertation at the Ludwig Maximilians University Munich, p. 48/49 (pdf)
- ↑ DLG working group forage and feeding: Supplement to the brochure “Balancing the nutrient excretion of farm animals” - DLG work / Volume 199 ( Memento of the original from October 12, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , January 2008
- ↑ a b German Association for Performance and Quality Tests
- ↑ Livestock practice up to date 6-2003 ( Memento from March 20, 2013 in the Internet Archive ) (PDF file; 207 kB)
- ↑ Walter Busch, Wolfgang Methling, Werner Max Amselgruber: Animal Health and Animal Disease Teaching , Georg Thieme Verlag, 2004, pp. 146-149, ISBN 9783830440925
