Effect of time on feed on performance of feedlot steers, carcass characteristics, and tenderness and composition of longissimus muscles.

Two hundred fifty-six British and Continental crossbred yearling steers (329 kg initially) were fed to study the effect of time on feed on live performance, carcass characteristics, tissue composition, and steak tenderness. Steers were divided into four slaughter groups and fed for either 105, 119, 133, or 147 d. Daily gains (carcass weight-adjusted basis) increased in a quadratic manner (P < .05; maximum at 119 d), whereas feed intake tended to increase linearly (P < .08) as cattle were fed longer. Feed conversion (carcass weight-adjusted basis) for steers fed 119 d was superior to that of steers fed for 147 d. Carcass weight, s.c. fat thickness, kidney, pelvic, and heart fat, overall carcass maturity, and yield grade increased linearly (P < .01) with time on feed. Marbling score and the percentage of cattle grading U.S. Choice increased (linearly; P < .01) with time on feed but at a decreasing rate (quadratic; P < .05). Cholesterol and total lipid concentrations in longissimus muscle increased linearly (P < .01) as time on feed increased, whereas the percentage of protein and moisture tended to decrease linearly (P < .10 and P < .01). Tenderness of ribeye steaks tended to increase linearly (P < .07) with time on feed, primarily due to a linear decrease (P < .03) in the percentage of steaks considered tough (shear force above 4.50 kg). Performance and carcass characteristics indicate that a feedlot finishing period of 119 to 133 d is ideal for British Continental crossbred yearling steers (329 kg).