EFFECT OF TIME ON FEED ON PERFORMANCE OF FEEDLOT STEERS, CARCASS CHARACTERISTICS, AND TENDERNESS AND COMPOSITION OF LONGISSIMUS MUSCLES

Two hundred fifty-six British Continental crossbred yearling steers (3 29 kg initially) were fed to study the effect of time on feed on live performance, carcass characteristics, tissue composition, and steak te nderness. Steers were divided into four slaughter groups and fed for e ither 105, 119, 133, or 147 d. Daily gains (carcass weight-adjusted ba sis) increased in a quadratic manner (P < .05; maximum at 119 d), wher eas feed intake tended to increase linearly (P < .08) as cattle were f ed 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 m aturity, and yield grade increased linearly (P < .01) with time on fee d. Marbling score and the percentage of cattle grading U.S. Choice inc reased (linearly; P < .01) with time on feed but at a decreasing rate (quadratic; P < .05). Cholesterol and total lipid concentrations in lo ngissimus muscle increased, whereas the percentage of protein and mois ture 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 ste aks considered tough (shear force above 4.50 kg). Performance and carc ass characteristics indicate that a feedlot finishing period of 119 to 133 d is ideal for British Continental crossbred yearling steers (329 kg).