Effects of backgrounding-phase rate of gain on performance and carcass characteristics of feedlot steers

Abstract

The objective was to evaluate effects of varying backgrounding-phase growth rates (BGR) on subsequent finishing-phase performance and carcass characteristics of feedlot cattle. Steers (n = 144) were randomly assigned to 1 of 3 BGR treatments from study initiation to 409 kg of BW. Treatments consisted of 0.91 kg/d (0.91ADG), 1.13 kg/d (1.13ADG), or 1.36 kg/d (1.36ADG). Net energy equations were used to prescribe sufficient DM to achieve desired BGR for each group. When each treatment reached the target BW of 408 kg at the end of the backgrounding phase, steers were transitioned to a finishing diet. From this point on, treatments were managed similarly. Steers within each treatment were slaughtered independently at a common 12th-rib fat endpoint. Backgrounding-phase ADG linearly increased (P < 0.01). The backgrounding phase lasted 76, 61, and 54 d for 0.91ADG, 1.13ADG, and 1.36ADG, respectively. Finishing-phase ADG and DMI linearly decreased (P ≤ 0.02) as BGR increased, with no difference in G:F (P ≥ 0.16). Cumulative ADG linearly increased with greater BGR (P = 0.02), and G:F also increased (P = 0.07). Restricting BGR linearly increased hot carcass weight (P = 0.04). Marbling score tended to respond quadratically to increasing BGR as it increased from 0.91ADG to 1.13ADG and then decreased between 1.13ADG and 1.36ADG (P = 0.05). Marbling scores responded quadratically (P = 0.05). Using a low BGR can result in improved finishing-phase performance and greater final BW; however, a greater number of days on feed is required. Increases in hot carcass weight also can be achieved with lesser BGR, although greatest carcass quality may be realized with only modest restriction in BGR.