Purdue University Agricultural Experiment Station Lafayette, Indiana
Mimeo AS-277 April 22, 1960 (Progress Report)
HIGH PROTEIN-UREA SUPPLEMENTS WITH AND WITHOUT LYSINE FOR FATTENING STEER CALVES 
T. W. Perry, W. M. Beeson and M. T. Mohler Department of Animal Science
A majority of the mixed protein supplements used in cattle rations contain from 30 to 32 percent protein. Recently, there has been a lot of interest in feeding supplements with high levels of protein (48 to 50 percent), whereby the extra protein equivalent is made up with urea. Theoretically, this should reduce the amount of protein supplement required to balance the ration. However, the limiting factor in the past has been that cattle cannot effectively meet more than one-third of their protein requirement from urea, and the remainder has to be furnished from natural proteins. If all of the nutrients necessary for bacterial synthesis of protein in the rumen can be identified, then it should be possible for cattle to meet their supplementary protein needs essentially from urea (non-protein nitrogen). When this barrier is conquered, then 1.0 pound of a 64$ (high-urea) supplement should give the same response in cattle as 2.0 pounds of a 32$ supplement.
Although all of the essential amino acids (components of protein) can be synthesized in the rumen by microorganisms from non-protein nitrogen (urea), there is a possibility that some one or more amino acids, such as lysine, are not produced in adequate amounts for maximum performance. In the past, we have assumed that amino acids were not a limiting factor in ruminant diets. This opens up a new field of research for critical evaluation.
This experiment was designed with the following objectives:
1.	To compare a 32, 40, 48, 56, 64 and 72 percent protein supplement when fed on the same protein equivalent basis to balance a ration for fattening steer calves.
2.	To determine the effect of feeding 10 grams of lysine per steer daily with the various supplements.
Experimental Procedure
Twelve lots of six Hereford steer calves each were fed on a basal ration of ground shelled corn (full-fed), 15 to 20 pounds of corn silage and modifications of Supplement A with urea at the same protein level. The protein content of each supplement was increased by adding urea (26 percent protein equivalent) and reducing the amount of soybean meal in the formula. L-lysine HC1 was added to the different supplements so that each steer would, receive 10 grams of lysine per head daily. Adjustments were made in the formula to compensate for the protein supplied by the lysine premix. The composition of the supplements is given in Table 1.
T7 Acknowledgement is made to Chas. Pfizer & Co., Terre Haute, Indiana, for "" furnishing the L-lysine HC1 for this experiment and also a grant-in-aid for the support of this research.