Effects of Source of Energy on Performance, Ultrasonic, Carcass, and Economic Characteristics of Early-Weaned Steers

Angus, Angus × Simmental (n = 200), and crossbred (n = 4-6) steers (BW = 128 ± 2 kg) were used to determine the effect of source of energy on performance, ultrasonic, carcass, and economic characteristics. Steers were early weaned (65 d) and randomly assigned by breed to a growing phase treatment: intermediate starch (IS), low starch (LS), or very low starch (VLS). Corn as a percentage of DM during the growing phase (111 d) decreased at 40, 20, and 0% for IS, LS, and VLS, respectively; during the finishing phase treatment (156 d), corn decreased at 50, 25, and 0% for IS, LS, and VLS, respectively. For the finishing phase, steers were randomly reallocated within pen to the IS, LS, or VLS treatment. As the starch level decreased in the growing phase diets, growing phase performance differences were NS (P > 0.51), but finishing phase DMI (P = 0.03) increased linearly and G:F was less efficient (P < 0.01). As the starch level decreased in the finishing phase diets, ADG decreased linearly (P < 0.01) and G:F became less efficient (P < 0.01). As an effect of the previous growing phase nutrition, marbling score (P < 0.01) and backfat decreased linearly (P = 0.02), whereas the finishing phase rate of marbling improved linearly (P < 0.01). As the starch level decreased in the finishing phase diets, the rate of backfat decreased linearly (P < 0.01) and the rate of marbling tended (P = 0.13) to decrease. As the level of starch decreased in both phases, cattle had linearly more desirable YG (P < 0.01), less desirable QG (P < 0.01), and decreased feed costs (P < 0.01). In this study, level of starch affected performance, ultrasonic, and carcass characteristics, and profitability differences were NS.