Nutrition  Beef
AS-386 March, 1969
Effective Utilizafton of Urea by Beef Cattle

W.M. Beeson and T.W. Perry, Animal Sciences Department
INTRODUCTION
The use of urea as a partial substitute for the protein requirements of ruminants is not new. In 1891 Zuntz recognized and presented evidence that microorganisms in the rumen could synthesize bacterial protein from non-protein nitrogen compounds such as urea. The shortage of natural protein supplements in Germany during World War I led to the extensive use of urea in dairy feeds in 1918 and was widely used in Europe in 1925- Urea was introduced into the United States in the thirties but was not accepted as an in -gredient in ruminant diets until the research of Hart and co- workers in 1937.
In the early fifties it was shown that urea could effectively replace 25 to 33 per cent of the protein nitrogen in cattle rations. However, the use of urea lagged and was not widely accepted until Beeson et at. (l96Ua), Garrigus (196U) and Conrad and Kibbs (1967) revealed that urea utilization by ruminants (beef cattle, dairy cattle and sheep) could be improved by combining urea with dehydrated alfalfa meal in a supplement.
Each year urea is replacing a larger per cent of the supplementary protein in cattle and sheep rations. Research at Indiana, Iowa, Illinois, Michigan, Minnesota and Tennessee has shown that 50 to 100 per cent of the supplementary protein can be furnished from urea. However, even with supplements where 90 per cent of the protein equivalent is from urea,
only about one-third of the total protein in the ration is supplied from non-protein nitrogen*, the remainder is supplied from grain and roughages. Eventually urea and/ or other non-protein nitrogen compounds will be used as the major sources of supplementary protein for ruminants.
Today urea or other non-protein nitrogen compounds can furnish 33 per cent of the total protein requirement of beef cattle; higher levels cause a depression in gain and feed efficiency.
In the past seven years the feed use of urea has doubled. The USDA predicts that the domestic sales of urea for feed use are expected to reach a level of 1955000 tons in 1970 — more than three times the 60,000 tons used in 1956.
NITROGEN METABOLISM AND PROTEIN SYNTHESIS
Urea is not a protein. It is only a

1)
simple nitrogen compound, NH -C-NII , from
2 2
which the microorganisms can obtain nitrogen, synthesize amino acids and finally bacterial protein provided that all the nutrients essential for protein synthesis are present. The use of urea as a substitute for natural protein gave poor and erratic results in its early history because too many workers did not recognize that a complicated array of nutrients are needed for optimum urea utilization.
1/ Part of this information was published in the Proceedings of the Distillers Peed Research Council, Vol. 2h, p. UU--51, March 5, 1969, Cincinnati, Ohio
Beef Section • Animal Sciences Department Cooperative Extension Service, PURDUE UNIVERSITY, Lafayette, Indiana