Protein levels and monensin for growing and finishing steers [Dietary protein level, carcass deposition]

One hundred sixty-eight Angus X Hereford crossbred beef steers were utilized to evaluate the influence of two levels of monensin (0 or 33 ppm) on three levels of dietary protein (9, 11 or 13% on a dry matter basis). The study was divided into a growing phase when steers received ad libitum corn silage and the needed protein supplement to supply the appropriate protein level. The finishing diet consisted of 85% dry corn and 15% corn silage plus a protein supplement to yield an 11% protein diet fed to all steers. Estimates of carcass composition were made at the beginning, at the end of the growing phase and at completion of the study. During the growing phase, growth rate (GR), dry matter intake (DMI) and efficiency of gain (F/G) were all improved (P less than .01) with increasing protein level, while monensin reduced (P less than .01) DMI and improved (P less than .01) F/G, with the greatest improvement coming on the 9% protein diet. The rate of protein deposition was increased (P less than .05) with increasing protein level and was increased (P less than .01) on the 9% protein diet while being reduced on the 13% protein diet when monensin was included in the diet. Previous protein level influenced steer performance during the finishing phase, with the steers previously receiving the 13% protein diet having the poorest GR and F/G while those having received the 11% protein diet having the highest GR.