TARGET FINISHING BEEF STEERS AND 1996 NRC BEEF MODEL EVALUATION

Abstract

Two trials were conducted to determine the effects of breed-type, backgrounding program, and endpoint on the feedlot and carcass performance of beef steers, and to evaluate the 1996 National Research Council (NRC) Beef Model. Trial 1 utilized 144 large frame, Charolais-cross (304.6 ± 16.3 kg) and 144 medium frame, Hereford-cross (294.8 ± 20.9 kg) steers while Trial 2 utilized 88 medium frame, Angus-cross (289.5 ± 15.0 kg), 88 large frame, Charolais-cross (299.8 ± 17.7 kg), and 88 medium frame, Hereford-cross (291.1 ± 20.9kg) steers. Within breed­ type, short (70 d) or long (126 d) backgrounding programs (Trial 1) and 6 or 12-mm ultrasound backfat endpoints (Trials 1 and 2) were assigned. Backgrounding ADG was restricted in both trials by limiting feed intake. Large frame steers were allowed greater (P≤ 0.05) backgrounding ADG but had poorer (P ≤ 0.05) finishing ADG. In both trials, carcass size was increased (P ≤ 0.05) by the large frame size, longer backgrounding, and the fatter endpoint. Lean meat yield was greater (P ≤ 0.05) for Charolais than for Hereford steers (Trial 1) and the leaner endpoint (Trials 1 and 2). Marbling was greater (P ≤ 0.05) for Angus (Trial 2) and Charolais (Trials 1 and 2) than for Hereford steers (Trials 1 and 2), and for the fatter endpoint (Trials 1 and 2). The DMI that was predicted by the 1996 NRC Beef Model was higher (P ≤ 0.05) than that which was observed during backgrounding (Trials 1 and 2). No difference (P > 0.05)existed between predicted and observed DMI during the finishing period (Trials 1 and 2). Regression analysis indicated accurate prediction of DMI (P > 0.05 biases= 0%) during finishing period in Trial 1 and the combined finishing periods of Trials 1 and 2. Predicted ADG was lower (P ≤ 0.05) than observed in all feeding periods. Breed-type, backgrounding program, and ultrasound backfat endpoints were effective in altering growth and targeting production goals for value-based marketing.