Effects of dietary ractopamine hydrochloride and zilpaterol hydrochloride supplementation on performance, carcass traits, and carcass cutability in beef steers.

British × Continental steers (initial BW = 484.6 kg) were fed at a commercial feed yard to evaluate the effects of ß-agonists on live performance, carcass characteristics, and carcass subprimal yield. Weights and ultrasonic measurements were used to allocate steers to pens (n = 40) divided equally into 4 blocks, with 2 treatment replicates per block. Pens were randomly assigned to 1 of 5 treatments: control; ractopamine-HCl (RH) fed at 200 or 300 mg • steer(-1) • d(-1), or 400 mg • steer(-1) • d(-1) top dress for the final 30 d of feeding; or zilpaterol-HCl (ZH) fed at 7.5 mg/kg beginning 23 d before slaughter with a 3-d withdrawal period. Steers were harvested by block at a commercial facility over 4 wk. Carcass based performance measures were calculated using initial pen weights and actual DMI. From each pen, eight carcasses that were within ± 13.6 kg of the mean pen HCW were selected such that two carcasses were within each of the following four Yield Grade (YG) ranges: YG ≤ 2.8; 2.9-3.2; 3.3-3.5; YG > 3.5. Carcasses were fabricated by plant personnel to determine subprimal yield. Steers fed ZH had higher carcass-based ADG and carcass-based G:F compared with all other treatments (P < 0.05). Carcass-based ADG and carcass-based G:F were higher in RH treatments compared with controls (P < 0.05). Steers fed ZH had higher dressing percentages (1.0 to 1.6%) and larger LM area (4.3 to 6.7 cm(2)) than all other treatments (P < 0.05). Use of RH 400 and ZH increased HCW 6.3 and 11.1 kg, respectively compared with controls (P < 0.05). Compared with controls, RH 300 and ZH decreased marbling score and the frequency of carcasses qualifying for upper 2/3 Choice premiums (P < 0.05). Beta-agonists increased subprimal yield from the round and loin; however, blade meat was the only cut from the rib or chuck affected by ß-agonists. Results from this study indicated improvements in performance and carcass traits as a result of ß-agonist use; however, differences between ZH, RH 400, and RH 300 treatments were minimal for carcass traits and cutability. Increases in saleable yield following ß-agonist use were not uniformly distributed across the four major primals and the majority of weight gain occurred in the lower priced cuts of the round and chuck. Increased response of the lower priced cuts to ß-agonists could have economic implications to packers.

Effects of ractopamine hydrochloride and zilpaterol hydrochloride supplementation on longissimus muscle shear force and sensory attributes of calf-fed Holstein steers.

The effect of ractopamine hydrochloride (RH) and zilpaterol hydrochloride (ZH) on slice shear force (SSF) and sensory characteristics of beef from calf-fed Holstein steers was evaluated. All steers were implanted with a progesterone (100 mg) plus estradiol benzoate (10 mg) implant followed by a terminal trenbolone acetate (200 mg) plus estradiol (40 mg) implant. Steers were blocked by weight into pens (n = 32) randomly assigned to 1 of 4 treatments: control, RH fed at 300 mg·steer(-1)·d(-1) (RH 300) or RH fed at 400 mg·steer(-1)·d(-1)(RH 400) for the final 31 d of finishing, or ZH fed at 6.8 g/t for 21 d with a 5-d withdrawal before harvest. Fourteen carcasses were randomly selected from each pen, and two LM samples (1 per side) were excised and aged either 14 or 21 d before SSF testing. For trained panel evaluation, two steaks were collected from each of 60 low Choice strip loins (20 each from control, RH 300, and ZH treatments) and aged either 14 or 21 d. Steers fed RH and ZH produced steaks with SSF values that were 9% to 25% higher than controls. No difference in SSF was detected between the two levels of RH (P > 0.05). Compared to controls, the probability of steaks aged 14 d failing to meet SSF requirements to be certified tender (SSF < 20 kg) was increased 0.15, 0.17, and 0.26 in steers fed RH 300, RH 400, and ZH, respectively. Compared to controls, the probability of steaks aged 21 d having SSF values >20 kg was increased 0.03, 0.08, and 0.16 in steers fed RH 300, RH 400, and ZH, respectively. Steaks from Select carcasses of steers fed ZH aged 21 d postmortem had double the probability (0.39 vs. 0.17) of having SSF values >20 kg compared to steaks from steers fed either level of RH (P < 0.05). This difference tended to be identical in steaks from Select carcasses 14 d postmortem (0.50 vs. 0.33; P = 0.11); however, no difference was found in low Choice samples at 14 or 21 d postmortem. Trained panelists rated steaks aged 14 d from steers fed ZH lower for overall tenderness and flavor compared to controls (P < 0.05); however, no difference was found between controls and those fed RH 300. Steaks from steers fed ZH aged 21 d were rated lower for overall tenderness and juiciness compared to controls and those from steers fed RH 300 (P < 0.05). This study suggests RH and ZH negatively impact sensory attributes of beef from calf-fed Holstein steers.

Effects of ractopamine hydrochloride and zilpaterol hydrochloride supplementation on carcass cutability of calf-fed Holstein steers.

Effects of ractopamine hydrochloride (RH) and zilpaterol hydrochloride (ZH) on saleable yield of carcass sides from calf-fed Holstein steers were evaluated using steers implanted with a progesterone (100 mg) plus estradiol benzoate (10 mg) implant followed by a terminal trenbolone acetate (200 mg) plus estradiol (40 mg) implant. Steers were blocked by weight into pens (n = 32) randomly assigned to one of four treatments: control, RH fed at 300 mg•steer(-1)/d(-1) (RH 300) or RH fed at 400 mg•steer(-1)/d(-1) (RH 400) the final 31 d of finishing, and ZH fed at 60 to 90 mg•steer(-1)/d(-1) (7.56 g/ton on a 100% DM basis) for 21 d with a 5 d withdrawal before harvest. Eight to nine carcass sides were randomly selected from each pen; carcass sides with excessive hide pulls, fat pulls or bruises were avoided. Cutout data were collected within a commercial facility using plant personnel to fabricate sides at a rate of one every 3 to 4 min into items typically merchandised by the facility. All lean, fat and bone were weighed and summed back to total chilled side weight with a sensitivity of ± 2% to be included in the data set. Compared to controls, ß-agonists increased saleable yield of whole-muscle cuts by 0.61%, 0.86% and 1.95% for RH 300, RH 400 and ZH, respectively (P < 0.05). Percent fat was less in carcasses from the ZH treatment compared to controls (P < 0.05); however, this difference was not observed between RH treatments and controls (P > 0.05). Percent bone was less in the ZH treatment due to increased muscle (P < 0.05). The percent of chilled side weight comprised of trimmings was unchanged between treatments, but on a 100% lean basis, RH 400 and ZH increased trim yields (P < 0.05). Analysis of saleable yield by primal showed a fundamental shift in growth and development. Beta-agonists caused a shift in proportion of saleable yield within individual primals, with a greater portion produced from the hindquarter relative to the forequarter, specifically in those muscles of the round (P < 0.05). Beta-agonists increased saleable yield, but these effects were not constant between all major primals. The cutout value gained by packers as a result of ß-agonist use may be influenced more by reduced fatness and increased absolute weight if musculature is primarily increased in the lower priced cuts of the carcass.