Effects of crude protein concentration in diets of feedlot steers fed to achieve stepwise increases in rate of gain

Two experiments were conducted to determine supplemental CP requirements fo r feedlot steers prescription-fed to achieve stepwise increases in ADG duri ng the feeding period. In Exp. 1, 106 steers (initial BW = 285.7 +/- 3.4 kg ) were allotted to 12 pens. Treatments consisted of ad libitum consumption of a 12% CP diet throughout the experiment (AL12%), prescription intake of a 12% CP diet (PI12%), or prescription intake of high-CP diets (PIHCP). The PIHCP diets were formulated to provide the same grams of CP per day as the AL12% diet. Steers in the prescription intake feeding regimens were fed to gain 1.13 kg/d for the first 87 kg of gain and 1.36 kg/d for the next 134 kg of gain and were offered feed for ad libitum consumption for the final 5 2 kg of gain before slaughter at 559 kg. Overall ADG was lower (P < 0.05) f or steers fed PI12% and PIHCP diets than for those fed the AL12% diet (1.48 and 1.50 vs 1.60 kg/d, respectively). Total DM intake was lower (P < 0.08) for steers fed the PI12% and PIHCP diets than for steers fed the AL12% die t (1,359, 1,370, and 1,421 kg, respectively). Dressing percentage, backfat thickness, and quality grade were lower (P < 0.05) for steers fed the PI12% and PIHCP diets than for steers fed the AL12% diet. In Exp. 2, 142 steers (initial BW = 285.4 +/- 3.1 kg) were allotted to 16 pens. System 1 was ad l ibitum consumption of a 12% CP diet throughout the experiment. Steers in Sy stems 2, 3, 4, and 5 were subjected to the same prescription intake strateg y as steers in Exp. 1. During the three phases of growth (1.13 kg/d, 1.36 k g/d, and ad libitum), steers were fed the following CP concentrations: Syst em 2(12, 14, and 12%); System 3(12, 14, and 14%); System 4(12, 16, and 12%) ; and System 5(12, 16, and 14%). No differences (P > 0.06) in total steer p erformance, carcass characteristics, or carcass chemical composition were o bserved among systems. Increasing percentage of CP in diets of prescription -fed steers to provide the same daily intake of CP as steers consuming feed ad libitum was not beneficial.