Utilization of Coproducts As an Alternative to Forage in Adapting Feedlot Cattle to Finishing Diets

The objective of this study was to determine the interaction of replacing forage with coproducts and the number of step-up diets when adapting feedlot cattle to a finishing diet. Simmental × Angus and Angus steers (N = 140; 237 ± 28 kg) were blocked by initial BW and allotted to 20 pens. Steers were fed a common receiving diet for the first 9 d after weaning. Then pens were assigned to 1 of 2 dietary treatments: 1) decreasing coproduct inclusions (soybean hulls and modified wet distillers grains) while increasing corn over 36 d or 2) decreasing forage inclusions (alfalfa and grass hay) while increasing corn over 36 d. Pens were fed either 5 or 2 step-up diets for each dietary treatment during the 36 d adaptation period in a 2 × 2 factorial design. Steers were fed a common finishing diet for the remainder of the trial (160 d). At d 36, steers fed the coproduct-based diets had a greater BW (319 vs. 313 kg; P = 0.01) and ADG (2.29 vs. 2.12 kg; P = 0.02) compared with steers fed the forage-based diets. Steers fed the coproduct-based diets had increased DMI (7.0 vs. 6.8 kg; P = 0.05) and tended (P = 0.08) to increase G:F over the initial 36 d. Steers fed the coproduct-based diets with 2 step-up diets had the greatest overall ADG (P ≤ 0.05) and final BW (P ≤ 0.05) compared with all other treatments at d 196. The number of step-up diets did not affect ADG (P = 0.47), DMI (P = 0.61), or G:F (P = 0.75) in the initial 36 d. There was a tendency for HCW (387 vs. 380 kg; P = 0.10) to be greater for steers fed the coproduct-based diets. Yield grade was greater (P = 0.02) for steers fed two step-up diets due to increased (P = 0.04) backfat thickness and smaller (P = 0.09) ribeye areas. Marbling score was not affected (P ≥ 0.61) by diet or number of step-up diets. The number of step-up diets before the finishing phase did not affect growth performance or feed conversion. Greater coproduct inclusions can be used in place of forage to increase growth performance during the adaption phase and increase ADG throughout the overall feeding period.