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.

Effects of ractopamine and trenbolone acetate implants with or without estradiol on growth performance, carcass characteristics, adipogenic enzyme activity, and blood metabolites in feedlot steers and heifers.

Two experiments were conducted to evaluate effects of ractopamine (RAC) and steroidal implant treatments on performance, carcass traits, blood metabolites, and lipogenic enzyme activity in feedlot cattle. In Exp. 1, yearling steers (n = 486; initial BW = 305 kg) were used in a 3 × 3 factorial arrangement of RAC doses of 0 (R0), 100 (R100), or 200 (R200) mg·steer(-1)·d(-1) fed for 28 d and implant regimens (implant-reimplant) of no implant-no reimplant (NI-NI), 120 mg of trenbolone acetate (TBA) and 24 mg of estradiol-17ß (E17B)-no implant (RS-NI), or 80 mg of TBA and 16 mg of E17B followed by 120 mg of TBA and 24 mg of E17B (RI-RS). Except for KPH and skeletal maturity score, no RAC × implant interactions were noted (P > 0.10). Carcasses from R200 were 6.3 kg (P = 0.042) heavier than those from R0. Marbling, calculated empty body fat (EBF), and USDA quality grade did not differ (P > 0.10) among RAC treatments. The RI-RS steers had 12.6 kg (P = 0.001) and 41.1 kg (P < 0.001) greater HCW than RS-NI and NI-NI, respectively. Despite no difference (P > 0.10) in EBF, marbling score was decreased for RI-RS (P < 0.001) and RS-NI (P = 0.001) relative to NI-NI, resulting in 14.6 and 11.4 percentage unit fewer USDA Prime and Choice carcasses with RI-RS (P = 0.008) and RS-NI (P = 0.039) than with NI-NI. In Exp. 2, heifers (n = 48; initial BW = 347 kg) were used in a 3 × 2 factorial arrangement of RAC doses of 0 (R0) or 250 (R250) mg·heifer(-1)·d(-1) and implant regimens of none (NI), 200 mg of TBA (TO), or 200 mg of TBA and 20 mg of E17B (TE). Blood samples were collected at various times during the feeding period, and subcutaneous adipose samples were collected on d 119. For growth and carcass measurements, no RAC × implant interactions (P > 0.10) were detected. The RAC-supplemented heifers had greater HCW (P < 0.10) with no difference in marbling score. For implant regimens, TE heifers had greater HCW than the NI (P = 0.001) and TO (P = 0.037) heifers. Although EBF did not differ among implant treatments (P > 0.10), TE (P = 0.021) and TO (P = 0.039) had fewer Choice carcasses than NI. Heifers with implants had decreased cortisol and increased IGF-1 and NEFA (P < 0.10) compared with NI heifers. An implant × RAC interaction was detected (P = 0.001) for serum urea nitrogen (SUN), with TE and RAC-supplemented heifers having decreased SUN. These data suggest that the effects of implant and RAC on growth and carcass traits are independent and that USDA quality grade and marbling score can differ significantly among carcasses with similar calculated EBF values.

The effect of rumen degradable and rumen undegradable intake protein on feedlot performance and carcass merit in heavy yearling steers.

A total of 432 crossbred yearling steers (395 kg +/- 6.35) were used in a randomized block experiment to study the effects of rumen degradable intake protein (DIP) and rumen undegradable intake protein (UIP) concentration on feedlot performance and carcass merit. The 6 dietary treatments used for this study included 1) a 10.5% CP diet with 5.1% UIP and 5.4% DIP (DIP5); 2) an 11.5% CP diet with 5.1% UIP and 6.4% DIP (DIP6); 3) a 12.5% CP diet with 5.1% UIP and 7.4% DIP (DIP7); 4) a 13.5% CP diet with 5.1% UIP and 8.4% DIP (DIP8); 5) a 14.5% CP diet with 5.1% UIP and 9.4% DIP (DIP9); and 6) a 14.5% CP diet with 6.1% UIP and 8.4% DIP with the additional UIP provided by corn gluten meal. There was a linear increase in final BW and ADG and a trend for a linear increase in DMI associated with increasing DIP concentration within the 5.1% UIP treatments. Feed efficiency and NE recovered from the diet were not influenced by dietary DIP concentration. As dietary DIP concentration increased, carcass fat depth and average yield grade increased linearly and the percentage of yield grade 1 and 2 carcasses decreased linearly. Dietary UIP treatment had no effect on final BW, ADG, DMI, G:F, and calculated NE recovery. For the 14.5% CP diets, marbling score tended to be reduced for steers fed 6.1% UIP as compared with 5.1% UIP. The remaining carcass traits were not affected by dietary UIP. The results of this study show that the DIP requirement in the finishing diet for heavy yearling steers fed steam-flaked corn is greater than 7.4% of dietary DM but likely is not more than 8.4% of dietary DM when dietary UIP is approximately 5.1% of dietary DM. Increasing UIP above 5.1% of dietary DM did not improve feedlot performance or HCW. Expressed on a CP basis, it appears as though the requirement for CP for heavy yearling steers fed steam-flaked corn-based finishing diets is 13.5% of DM, with approximately 62% of CP from DIP.

Effect of dietary supplemental vitamin A concentration on performance, carcass merit, serum metabolites, and lipogenic enzyme activity in yearling beef steers.

A randomized complete block design experiment with 360 single-source black yearling steers (average BW = 316.1 +/- 9.1 kg) fed a 91% concentrate (steam-flaked corn base) diet was conducted to evaluate the effects of supplemental vitamin A (0, 1,103, 2,205, 4,410, or 8,820 IU/kg of dietary DM) on plasma and liver vitamin A and E concentrations, lipogenic enzyme activity, marbling score, and performance of yearling steers. Final BW (586, 580, 590, 585, and 584 kg for 0, 1,103, 2,205, 4,410, and 8,820 IU of supplemental vitamin A/kg of DM, respectively) did not differ (P = 0.39) among treatments. Feed efficiency, ADG, and daily DMI did not differ (P > 0.10) among treatments within each 28-d period or for the overall experiment. From d 57 to slaughter, average DMI (10.33, 10.28, 10.57, 9.75, and 10.22 kg/steer daily for 0, 1,103, 2,205, 4,410, and 8,820 IU of vitamin A/kg of DM, respectively) was less (P < 0.02) by steers receiving 4,410 IU of supplemental vitamin A/kg of dietary DM than for steers in the other treatments. Furthermore, DMI was greater (P = 0.06) for steers receiving 2,205 IU of supplemental vitamin A/kg of dietary DM than for steers receiving 8,820 IU of supplemental vitamin A/kg of DM. Marbling score, HCW, LM area, and 12th-rib fat thickness did not differ (P > 0.10) among treatments. Similarly, the percentage of carcasses grading >or=USDA Choice (62.6, 52.8, 64.0, 58.4, and 58.4% for 0, 1,103, 2,205, 4,410, and 8,820 IU of vitamin A/kg of DM, respectively), Select, or 0.10) among treatments. Except for d 56 (P = 0.050; r = 0.18 for liver retinol), no correlations (P > 0.10) between marbling score and any plasma or liver tissue retinol or alpha-tocopherol concentrations or vitamin A intake were found, and no differences (P > 0.10) in lipogenic enzyme activity were detected among treatments. Taken together with previous and concurrent research, results of this experiment suggest that vitamin A supplementation at a concentration up to twice the NRC recommendation has little effect on performance, marbling, or lipogenic enzyme activity in adipose tissue samples in yearling feedlot steers, and that 2,205 IU of supplemental vitamin A/kg of DM (20,000 IU/steer daily) or less is adequate to meet the vitamin A requirements of finishing beef cattle.

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness.

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW > or = 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-beta (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.

Effects of dietary level of ruminally protected choline on performance and carcass characteristics of finishing beef steers and on growth and serum metabolites in lambs.

Ruminally protected choline (RPC) was evaluated in two experiments. In Exp. 1, beef steers (n = 160; average initial BW = 350.9 kg) were fed a 90% concentrate diet with either 0, .25, .5, or 1.0% RPC (DM basis) for 112 to 140 d. Feeding .25% RPC increased ADG 11.6% compared with 0% RPC, but responses diminished with increasing RPC level (cubic response, P < .10). Daily DMI was not affected by RPC level, but feed:gain was improved 6.8% with .25% RPC compared with 0% RPC, and responses diminished with increasing RPC level (cubic response, P < .10). Carcass yield grade increased linearly (P < .10) as RPC level increased, but marbling score was lower for all three RPC-containing diets than for the 0% RPC diet (quadratic response, P < .05). In Exp. 2, 20 Suffolk lambs (initial BW = 29.8 kg) were fed an 80% concentrate diet for 56 d with the same RPC levels as in Exp. 1. Serum triglycerides (TG) and cholesterol (CLSTRL) were measured in weekly blood samples, and intensive blood samples were collected on d 28 and 56 to evaluate serum insulin (INS), GH, and NEFA. For the 56-d feeding period, ADG responded quadratically (P < .10) to RPC level, but DMI and feed:gain were not affected. Serum INS and NEFA concentrations increased linearly (P < .05) and serum GH responded cubically (P < .05) to RPC level on d 28, but no differences were noted on d 56. Serum TG concentrations in weekly samples increased linearly (P < .10) with RPC level, but, averaged over all weeks, serum CLSTRL concentrations did not differ (P > .10) among treatments. Quantities of carcass mesenteric (P < .05) and kidney fat (P < .10) increased linearly, but longissimus muscle and liver fat contents did not differ (P > .10) among RPC levels. Supplementing RPC in high-concentrate diets improved performance, but results were not consistent among RPC levels or between cattle and sheep. Potential effects of RPC might be mediated through alterations in fat metabolism and(or) metabolic hormones related to fat metabolism.