Nitrogen in cow

Nitrogen leaves cow’s body in a form of milk protein and urea. Most of protein in feeding is resolved in a rumen, whereas some protein is sustainable and is digested later in the small intestine. There has to be enough energy in a rumen to resolve all the fast protein correctly. Protein is first turned into ammonia and if there isn’t enough energy the extra ammonia is absorbed in the bloodstream and turned into urea. The urea leaves cow in milk and urine but some of it returns to a rumen in saliva to be used again. The amount of urea going to waste is smaller when a cow produces more saliva to chew high-structure roughage.

Urea

The amount of urea can be measured in milk and it can be used in defining the nitrogen efficiency.

Urea content in milk (mg/dl)	Result	Observation
< 15	Too low	Production and milk protein lower
15–20	Slightly low	High N-efficiency, possibly lower production
20–30	Good	Very efficient production
30–35	Slightly high	Lower N-efficiency, production still increases
> 35	Too high	Problems with fertility, low N-efficiency

The farmers we met wanted to keep the nitrogen usage efficient so that there wouldn't be too much mineral losses. Most of the farmers we met followed their cattles' average urea levels and changed the feeding according to that. The solutions to improve the protein efficiency given us by the farmers can be found here.

Common things about urea

Urea is a simple compound that contains 46.7 percent nitrogen. It is found in many plants and is a normal end product of protein metabolism in mammals. A part of the urea produced in an animal's body is returned to the digestive tract in the saliva. The remainder of the urea is passed off in the urine as waste.

One pound of pure urea furnishes as much nitrogen as 2.92 pounds of protein (protein equivalent of 292 percent). The feed grade of urea has other ingredients, such as kaolin, wheat middlings, rice hulls or limestone, added to it to prevent caking and lumping. This material lowers the protein equivalent to 281, 283, 287 or 262 percent, depending on the amount added. The 281 urea is the most common.

Urea can be fed to ruminants as an economical replacement for a part of the protein in a ration.
The amount of urea a ruminant animal can use depends on the digestible energy or total digestible nutrients (TDN) content of the ration.
No more than 45g to 112,5g urea per head per day should be fed to feedlot cattle consuming a high concentrate ration.
Toxicity should not be a problem if urea is fed according to recommendations.
Vinegar is a helpful emergency treatment for urea poisoning if the animal is treated before tetany develops.

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Page updated 16.5.2006