Urea Levels, Protein and Diethylstilbestrol for Growing Steers Fed Purified Diets

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Abstract
Growth and metabolism trials were conducted using steer calves to determine the optimum level of urea needed in the purified diet for growth and nitrogen retention. Secondary objectives were to determine the influence of replacing 15% of the dietary urea nitrogen with isolated soy protein and the influence of diethylstilbestrol (DES) implantation on animal performance. Ruminal ammonia, the apparent digestibility of the dietary nitrogen and blood urea concentrations increased linearly as the crude protein equivalent (CPE) in the diet increased from 9.2, 14.0, 18.4 to 23.0%. Blood plasma serine, glycine and hydroxyproline decreased in a linear manner with increasing nitrogen levels. The 14.0% CPE diet promoted the most rapid growth of the four CPE levels when fed ad libitum in two growth studies. Steers fed 15% of their dietary nitrogen as isolated soy protein gained 0.62 vs. 0.57 kg daily for steers fed no isolated soy protein. DES-implanted steers gained 0.65 vs. 0.54 kg daily for controls. Data from two metabolism trials with restricted feed intake indicate that the greatest nitrogen retention was obtained with the 18.4% CPE diet.

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