Effect of extended days on feed on carcass gain, efficiency, and quality of individually fed beef steers.

Crossbred steers ( n  = 114, initial BW = 334 kg; SEM = 5 kg) were serially harvested to evaluate the change in carcass composition by feeding cattle 21 or 42 d longer than the 2014 industry average subjective measure of finish, 1.27 cm of 12th rib fat thickness. Carcass ultrasound measurements were collected on 76 steers at 1, 78, and 134 days on feed (DOF) to project appropriate harvest date. Steers were sorted into three harvest groups, and serially harvested at 142, 163, or 185 DOF, with the first harvest date selected based on an estimated 12th rib fat thickness of 1.27 cm via ultrasound measurement. Steers were fed using an individual animal feeding system, to determine individual performance metrics. Steer DMI did not differ ( P  ≥ 0.31) between harvest groups, while carcass-adjusted ADG and G:F decreased linearly ( P  ≤ 0.04) as DOF increased. Carcass weight increased linearly ( P  < 0.01) as DOF increased from 142 to 185 DOF, with steers gaining an additional 36 kg of HCW when fed an additional 42 DOF. Carcass LM area quadratically increased ( P  = 0.04) to 163 DOF and remained constant to 185 DOF. Marbling score was not different ( P  = 0.14) between harvest groups; however, the opportunity to grade USDA Premium Choice was improved for steers fed to 185 DOF. Calculated YG and 12th rib fat thickness increased linearly ( P  < 0.01) as DOF increased, with distributions across YG 1 through 5 differing between harvest groups ( P  < 0.01), and 185-d carcasses having the greatest frequency of YG 4 carcasses. As cattle are fed for additional DOF, live ADG and G:F decline, while HCW and LM area increase.