Factors Influencing the Performance of Feedlot Steers Limit-Fed High-Concentrate Diets

Abstract

Two experiments were conducted to determine the percentage of concentrate required in limit-fed growing diets for optimal finishing-phase performance. A third experiment was conducted to evaluate the effect of manger-space allowance on performance by limit-fed steers. In Exp. 1, 108 steers (average initial BW = 250 kg) were grown on 60 (60G), 75 (75G), or 90% (90G) concentrate limit-fed diets for 92 data prescribed rate of 1.0 kg/d, then finished on a 90% concentrate diet (90F; 140 d). Treatments were compared using linear (L) and quadratic (Q) contrasts. Beginning the finishing phase, 60G and 75G steers weighed less (Q, P=0.05) than the 90G steers; however, because the 75G steers grew at a faster rate (Q, P =0.02), they were heaviest (Q, P=0.04) at the end of the finishing phase. Increasing the percentage of concentrate in the growing diets tended (L, P=0.16) to increase DMI during finishing, hot carcass weight (L, P=0.14), and dressing percentage (L, P=0.16). Increasing the percentage of concentrate in the growing diet also increased (L, P=0.10)) marbling score, fat thickness, and USD A yield grade. In Exp. 2, 118 steers (average initial BW = 280 kg) were allotted to the 60G, 75G, and 90G limit-fed diets for 84 d, then finished on the 90F diet (168 d), or a fourth group was fed the 90F diet for 210 d. During the finishing phase, there was little evidence (P>0.24) that growth rate differed among treatments. The 90F steers averaged less DMI (P =0.03) than limit-fed cattle, resulting in a superior (P<0.001) feed:gain ratio compared with 60G, 75G, and 90G steers. No carcass measurements differed (P>0.13) among treatments. In Exp. 3, 272 steers (average initial BW = 227 kg) were limit-fed an 85% concentrate diet to gain a prescribed rate of 1.07 kg/d and allotted to 12.7, 20.3, 27.9, and 35.6cm of manger space per steer for an 84-d growing period. Decreasing the manger space allowance did not affect (P>0.14) daily gain, daily DMI, or feed:gain. After the 84-d growing period, within-pen variation in BW was positively associated (P<0.02) with increasing manger space allowance. Steers grown from approximately 240 to 370kg of BW produced high quality carcasses regardless of the percentage of concentrate in the growing diet. For largeframed steers, a growing phase seemed unnecessary. Restricting manger space to as little as 12.7cm per steer did not seem to increase within-pen variation in BW or decrease daily gain.