Fed Ractopamine Hydrochloride Research Articles

97 Use of genomic testing for predicting performance of finishing steers

Abstract Genomic testing is a commercially available tool that has the potential to be beneficial in selecting cattle for retained ownership, as well as making management and marketing decisions after finishing. The objectives of this study were to determine if commercially available genomic tests are predictive of differences in finishing performance of steers from sires selected based on divergent growth and milk EPDs. The commercial genomic testing of milk and average daily gain (ADG) scores used in the current experiment were based on Neogen Igenity Beef test results. Two trials were conducted at the OSU Willard Sparks Beef Research Center in Stillwater, Oklahoma. These experiments used two sets of steers from the OSU Range Cow Research Center (400 ± 13 kg, n = 154) from a spring calving cowherd (South Range Unit) and a fall calving cowherd (North Range Unit) of primarily Angus ancestry. Following preconditioning and a wheat pasture stocker program (South Range) or dry lot growing period (North Range), steers were allocated into pens (n = 5 animals/pen) by Igenity ADG Score: low growth (LG) had scores ranging from 1 to 4, medium growth (MG) had scores from 5 to 6, and high (HG) had scores from 7 to 10. Steers were blocked by initial BW and fed a step-up diet for 30 d before being switched to a finishing ration diet (8% prairie hay, 20% Sweet Bran, 62% dry-rolled corn, 5% liquid supplement, and 5% dry supplement [DM basis]). Cattle were fed ractopamine hydrochloride for 30 d before slaughter. The heavy block was on feed for an average of 136 d, while the light block was on feed for an average of 160 d. Data were analyzed as a randomized complete block design using the mixed procedure of SAS (SAS Inst. Inc., Cary NC) with pen as the experimental unit and finishing pen within block as the random statement. During the feeding period, HG steers gained more rapidly than MG or LG steers, with ADG of 2.08, 1.94, and 1.90 kg/d, respectively (P = 0.04). Because gains were greater, BW at slaughter for the HG steers was greater than MG and LG, averaging 690, 669, and 660 kg, respectively (P = 0.04) and hot carcass weights were greater for HG than MG and LG, averaging 438, 426 and 418 kg, respectively (P = 0.02). There were no other differences (P > 0.19) in carcass characteristics among steers. These data suggests that the genomic testing is accurate predictor of performance and can be used by producers can make better marketing decisions in selecting cattle for the retained. Genomic testing could be very beneficial for producers looking to minimize risk and maximize performance in their herd.

Feeding Ractopamine Improves the Growth Performance and Carcass Characteristics of the Lard-Type Mangalica Pig.

Mangalica pigs are gaining popularity within the U.S. as a niche breed, given their reputation for superior-quality pork. However, slow growth rates, a poor lean yield, and excessive adiposity limit the widespread adoption of Mangalica. To determine if feeding the metabolic modifier, ractopamine hydrochloride (RAC), would improve growth performance without impairing pork quality in the Mangalica, pigs were fed either 0 or 20 mg per kg RAC for 21 days. At 24 h postharvest, pork quality and carcass composition measurements were recorded; then, primal cuts were fabricated and assessed. RAC increased ADG (p < 0.04) and gain efficiency (p < 0.03) by 24% and 21%, respectively. RAC increased Loin Eye Area (p < 0.0001) by 21% but did not impact the 10th rib fat depth (p > 0.90) or marbling score (p > 0.77). RAC failed to alter any primal cut weights. Feeding RAC lowered b* values (p < 0.04) and tended to lower L* values (p < 0.08) while not affecting a* values (p > 0.30), suggesting RAC darkened loin color. Finally, RAC decreased cook yield percentage (p < 0.02) by 11% without impacting Warner-Bratzler Shear Force (p > 0.31). These data support the hypothesis that feeding RAC to Mangalica improves growth performance without impairing pork quality in this breed.

383 Effect of Feeding Ractopamine to Finisher Lard-Type Mangalica Pigs on Longissimus Muscle Fiber Myosin-Heavy Chain Isoform Expression and Cross-Sectional Area

Abstract Heritage breeds such as Mangalica pigs are gaining popularity in US niche markets and currently sold as high-quality meat due to greater meat quality characteristics. Research has demonstrated that feeding the β-adrenergic agonist ractopamine hydrochloride (RAC), stimulates hypertrophic growth of type-2, fast-twitch glycolytic muscle fibers via mTOR signaling resulting in greater myofibrillar protein synthesis. Therefore, the current study evaluated the effect of feeding RAC to Mangalica pigs during the finisher phase on longissimus muscle fiber myosin heavy-chain (MHC) isoform expression and cross-sectional area. Mangalica pigs were randomly assigned finisher diets for 21 d with 20 ppm (RAC; n = 8) or without (CTL; n = 6). Longissimus muscle samples were collected during carcass fabrication, flash-frozen in liquid nitrogen and stored at -80 °C. Immunofluorescence staining of 5-µm-thick cryosections to identify Type-1 (Developmental Studies Hybridoma Bank (DSHB) antibody Ba-D5), Type-2a (DSHB SC-71), and 2x (DSHB BF-35) MHC positive fibers. Type 2b fibers were determined by subtraction. Fibers in each image (≥ 150) were assessed for fiber type and their cross-sectional area (CSA) at 200X magnification. Data were analyzed as a one-way ANOVA using the GLIMMIX procedure of SAS V9.4. Means were separated with the PDIFF option and declared different when P ≤ 0.05. Tendencies were declared when 0.0501 ≤ P ≤ 0.1000. Feeding RAC decreased the density of Type 2a (P = 0.0136) and Type 2b (P = 0.0186) fibers in the longissimus muscle of Mangalica pigs. A tendency for RAC to reduce the density of Type 1, slow-twitch (6.61 vs. 16.14 fiber per mm2; P = 0.0505) fibers and increase the density of primarily oxidative fibers expressing a combination of Type 1 + Type 2a MHC isoforms (10.23 vs. 2.88%; P = 0.0524) was also observed. When analyzed as a proportion of total fibers, RAC reduced the proportion of fibers expressing only Type 2a (11.8 vs. 6.70%; P = 0.0468) and Type 2b (0.19 vs. 1.32%; P = 0.0101) MHC isoforms but increased the percentage of fibers expressing both Type 1 + Type 2a MHC isoforms (4.66 vs. 1.13%; P = 0.0280). Feeding RAC did not impact the density or proportion of fibers expressing Type 2x MHC (P ≥ 0.386). Mean longissimus muscle fiber CSA was not impacted by feeding Mangalica pigs RAC for 21 d (P = 0.4815). The CSA of the smallest and largest fibers nor fiber distribution were influenced by RAC inclusion in the diet of Mangalica pigs (P ≥ 0.484). In conclusion, feeding RAC Mangalica pigs impacted fiber MHC isoform expression in the longissimus muscle without altering fiber CSA. Future studies will explore the impact of RAC on the CSA of the various fiber types as well as the impact on other muscles in the Mangalica pig.

Effects of feeding ractopamine hydrochloride with or without supplemental betaine on live performance, carcass and meat quality traits, and gene expression of finishing pigs

The objective of this study was to evaluate the effects of ractopamine and betaine, supplemented alone or in combination, on live performance, carcass and meat quality traits, and gene expression (in both skeletal muscle and subcutaneous adipose tissue) of finishing pigs. Seventy-two pigs averaging 89.0 ± 3.44 kg were assigned to a control diet (CTRL-without ractopamine and betaine); CTRL+20 mg/kg ractopamine (RAC); CTRL+2.5 g/kg betaine (BET); or RAC + 2.5 g/kg betaine (RAC + BET). Pigs fed RAC and RAC + BET had greater average daily gain and carcass yield compared to CTRL. Pigs fed RAC, BET, and RAC + BET had greater loin muscle area, while backfat thickness was lower in pigs fed RAC + BET compared to CTRL. Pork from BET had lower shear-force and greater intramuscular fat content compared to CTRL. Regarding adipose tissue, RAC and BET increased expression of genes related to lipolysis and β-oxidation. These data indicate that performance and carcass traits of pigs can be improved with ractopamine, whereas betaine (when fed independently from ractopamine) increased the loin muscle area and pork quality.

Effects of dietary copper supplementation on performance, carcass characteristics, and lipolytic rate of beef steers fed ractopamine hydrochloride

Effects of dietary copper supplementation on performance, carcass characteristics, and lipolytic rate of beef steers fed ractopamine hydrochloride

Effect of ractopamine hydrochloride on environmental gas emissions, growth performance, and carcass characteristics in feedlot steers.

With a growing global population and increased environmental concerns around animal agriculture, it is essential to humanely maximize animal performance and reduce environmental emissions. This study aims to determine the efficacy of feeding ractopamine hydrochloride (RAC), an orally active, β 1-adrenergic agonist (β1AA), to feedlot steers in the last 42 d of finishing to reduce ammonia (NH3) emissions and improve animal performance. A randomized complete block design was used to allocate 112 Angus and crossbred Angus steers (initial body weight [BW] = 566.0 ± 10.4 kg) to 8 cattle pen enclosures. Pens (n = 4 per treatment, 14 steers per pen, and 56 steers per treatment) were randomly assigned to one of two treatments: 1) CON; finishing ration containing no RAC, 2) RAC; finishing ration containing 27.3 g/907 kg dry matter (DM) basis RAC. Steers were weighed on day −1 and 0 before treatment and day 14, 28, and 42 during treatment. Treatment rations were mixed and delivered daily by masked personnel. Measured emissions included NH3, nitrous oxide (N2O), methane (CH4), hydrogen sulfide (H2S), and carbon dioxide (CO2). The primary response variables assessed were emissions standardized by live weight (LW) and hot carcass weight (HCW). Steers were harvested on day 43 and carcass data were collected on day 43 and 44. Steers fed RAC reduced NH3 emissions by 17.21% from day 0 to 28 (P = 0.032) and tended to reduce NH3 from day 0 to 42 by 11.07% (P = 0.070) vs. CON. When standardized for LW, NH3 was reduced by 23.88% from day 0 to 14 (P = 0.018), 17.80% from day 0 to 28 (P = 0.006), and 12.50% for day 0 to 42 (P = 0.027) in steers fed RAC vs. CON. Steers fed RAC had 14.05% (P = 0.013) lower cumulative NH3 emissions when standardized by HCW vs. CON. Feeding RAC to Steers reduced H2S by 29.49% from day 0 to 14 (P = 0.009) and tended to reduce H2S over day 0 to 28 by 11.14% (P = 0.086) vs. CON. When H2S emissions were standardized for LW, RAC fed steers had a 28.81% reduction from day 0 to 14 (P = 0.008) vs. CON. From day 0 to 42 the RAC fed steers tended to have a 0.24 kg/d greater average daily gain (ADG) (P = 0.066) and tended to eat 4.27% less (P = 0.069) on a DM basis vs. CON. The RAC fed steers had a 19.95% greater gain to feed ratio (G:F) compared to CON (P = 0.012). Steers fed RAC had an average of 12.52 kg greater HCW (P = 0.006) and an increase of 1.93 percentage units in dressing percent (DP) (P = 0.004) vs. CON. Ractopamine is an effective medicated feed additive for reducing NH3 and improving end product performance through HCW yields.

Effects of ractopamine hydrochloride on nutrient digestibility and nitrogen excretion of finishing beef cattle.

The objective was to quantify the effects of the beta-adrenergic agonist (β-AA) ractopamine hydrochloride (Actogain, Zoetis, Parsippany, NJ) on nitrogen excretion and nutrient digestibility in feedlot cattle. In experiment 1, 12 Simmental × Angus steers were blocked by bodyweight (531 ± 16 kg) and used in a randomized complete block design. Dietary treatments included: 1) a control without β-AA (CON) or 2) 400 mg/steer/d ractopamine hydrochloride (RAC) for 35 d before slaughter. Diets contained (DM basis) 55% dry-rolled corn, 20% corn silage, 15% modified wet distillers grains with soluble, and 10% supplement. For each block, total collection of feed, orts, feces, and urine were conducted for two 5 d sampling periods during week 2 and 4 of RAC supplementation. No interaction (P > 0.21) between treatment and collection period was observed for any parameter evaluated. Dietary treatment had no effect (P = 0.51) on DMI, but RAC had decreased fecal DM output (P = 0.04) compared with CON. Thus, RAC had greater apparent total tract DM digestibility (77.2 vs. 73.5%; P < 0.01), N digestibility (72.4 vs. 69.4%; P = 0.01), and NDF digestibility (65.6 vs. 60.2%; P < 0.01) than CON. Although treatment did not affect nitrogen intake (P = 0.52), RAC tended to reduce total nitrogen excretion (113.3 vs. 126.7 g/d; P = 0.10) compared with CON due to a tendency for decreased fecal nitrogen output (53.9 vs. 61.3 g/d; P = 0.10). However, dietary treatment had no effect (P = 0.53) on urinary nitrogen output or percentage of urinary nitrogen excreted as urea (P = 0.28). Experiment 2 was an in vitro experiment conducted to validate the effects of RAC on nutrient digestibility using Simmental × Angus heifers (451 ± 50 kg). Rumen fluid was collected individually by stomach tube from CON- (n = 9) and RAC-fed (n = 10) heifers to inoculate bottles containing a CON or RAC-containing substrate in a split–plot design. No interaction between rumen fluid source and in vitro substrate was observed. Greater IVDMD (P = 0.01) was observed in rumen fluid from RAC-fed heifers compared with rumen fluid from CON-fed heifers. The inclusion of RAC in the in vitro substrate increased IVDMD (P < 0.01). Overall, feeding RAC increased microbial digestion of the dry-rolled corn-based finishing diet to increase total tract dry mater digestion by 5% and reduce nitrogen excretion by 10.6% in the 35 d period prior to slaughter.

291 Influence of feeding amino acid complexes of zinc and copper on growth performance and carcass response of finishing steers fed ractopamine hydrochloride

Abstract A 42-d research study evaluated effects of feeding beef steers increasing levels of dietary Zn from Zn methionine (AAC-Zn; ZINPRO, Zinpro Corporation, Eden Prairie, MN) with or without supplemental Cu from Cu amino acid complex (AAC-Cu; Availa Cu, Zinpro Corp.) concurrently with ractopamine hydrochloride (RAC; Optaflexx, Elanco Animal Health, Greenfield, IN). One hundred-twenty steers (mean BW = 624 kg), ≤ 50 d from projected harvest were randomized to three pens (40 steers/pen) equipped with GrowSafe Systems (Calgary AB, Canada) feed bunk technology. Each pen was assigned to one of three treatment diets: 1) basal finishing diet + 30 mg Zn/kg DM from AAC-Zn (CON); 2) basal finishing diet + 90 mg Zn/kg DM from AAC-Zn (AAC-Zn90); or 3) AAC-Zn90 diet + 10 mg Cu/kg DM from AAC-Cu (AAC-Zn/Cu). Following allocation to treatments, cattle were acclimated to pen cohorts and GrowSafe feed bunks for 7 days. All steers were fed 300 mg RAC∙hd-1∙d-1 starting 35 d prior to harvest. Individual feed intake measurements began with RAC feeding and continued for 35 d until cattle were shipped for harvest. Carcass data were collected from each steer. Data were analyzed with individual animal as the experimental unit using PROC MIXED and PROC GLIMMIX procedures of SAS 9.4 (SAS Institute, Cary, NC). Numerically AAC-Zn90 fed cattle had heavier carcass weights than CON and AAC-Zn/Cu. Steers fed AAC-Zn90 had greater (P = 0.02) marbling scores compared to AAC-Zn/Cu. Steers fed AAC-Zn90 had lower backfat thickness (P = 0.02) and numerically greater marbling scores compared to CON. A biphasic program of feeding a lower level of AAC-Zn for the duration of the finishing phase followed by an increased rate of AAC-Zn during RAC feeding may optimize overall live and carcass response and improve total individual animal value.

396 Effect of zinc amino acid complexes on growth performance and carcass characteristics of finishing beef steers fed with or without ractopamine hydrochloride- a nine study pooled analysis

Abstract A nine-study retrospective pooled analysis was conducted to evaluate supplemental Zn provided as an amino acid complex (ZnAA) on growth performance, carcass quality and yield in finishing beef steers fed with or without ractopamine hydrochloride (RAC) prior to slaughter. Data from nine well-controlled studies conducted at university and commercial feedlot research facilities in AB, IA, KS, OK and TX were evaluated using 249 pens ranging from 6 to 275 steers /pen (Total number=14,096 animals.; initial BW = 340± 6.2 kg). Treatments evaluated were: (1) Control (CON) =basal diet with 0 to 11 mg-1·kg-1 DM ZnAA and no RAC; (2) RAC = 200 to 320 mg RAC ∙hd-1∙d-1 fed 28 to 42 d prior to slaughter; (3) ZnAA only =30 to 120 mg-1·kg-1 DM fed throughout finishing period; (4) ZnAA + RAC. Main effects of feeding RAC, ZnAA and RAC × ZnAA interaction were determined for growth performance and carcass data with pen as experimental unit and initial BW as covariate. Combined analyses indicated no RAC × ZnAA interactions (P ≥ 0.23). RAC main effect improved carcass-adjusted growth performance and increased HCW and ribeye area (P ≤ 0.01). Main effect ZnAA increased carcass-adjusted final BW, ADG, and HCW (P ≤ 0.01); improved carcass-adjusted Gain: DM feed ratio (P = 0.06), dressing percentage (P = 0.02), and increased calculated yield grade, backfat thickness and percentage of carcass internal fat (P ≤ 0.10). A RAC × ZnAA interaction (P ≤ 0.10) was observed for USDA quality and yield grade distribution of carcasses. Incidence and severity of liver abscesses were reduced (P ≤ 0.05) by feeding either ZnAA or RAC. Feeding ZnAA and RAC to finishing cattle separately or in combination were additive for producing incremental improvements in production and carcass traits of economic importance.

401 Effect of zinc source and ractopamine hydrochloride on the growth performance and carcass characteristics of steers fed in confinement to harvest

Abstract Four hundred and thirty-two beef steers (346.3 ± 63.7 kg BW) were used to determine the effects of Zn source on feedlot cattle fed ractopamine hydrochloride. Cattle were blocked in groups of 54 by BW and housed in 48 pens containing 9 steers per pen. Pens within a weight block were randomly assigned to treatments in a 2 x 3 factorial arrangement, with factors being: 1) 0 or 30.1 mg of ractopamine HCl/kg DM fed during the final 29 days on feed; and 2) Zn source: 90 mg of supplemental Zn/kg DM from ZnSO4; Zn sulfate (67%) + Zn methionine (33%); and Zn from Zn hydroxychloride, fed through the entire feeding period. Cattle were fed a high concentrate finishing diet for 154 d and slaughtered at a commercial abattoir. Average daily gain, DMI, feed efficiency and carcass characteristics were determined after slaughter. Zinc source had no impact on live animal performance. Cattle fed ractopamine HCl had greater (P &amp;lt; 0.01) final BW, greater (P &amp;lt; 0.001) ADG, improved (P &amp;lt; 0.001) G:F, heavier (P &amp;lt; 0.01) HCW, and larger (P &amp;lt; 0.05) longissimus muscle compared to non-ractopamine supplemented steers. There was a Zn source by ractopamine interaction (P &amp;lt; 0.01) for dressing percentage. Cattle receiving ractopamine HCl with Zn hydroxychloride had a greater dressing percentage (P &amp;lt; 0.05) when compared to ractopamine HCl cattle fed other Zn sources. Cattle receiving ractopamine HCl with Zn sulfate had a lesser dressing percentage (P &amp;lt; 0.05) when compared to ractopamine HCl cattle fed other Zn sources. Additional Zn source by ractopamine HCl interactions were not significant. These data indicate that Zn source has minimal impacts on feedlot steer performance and carcass characteristics when supplemented to cattle receiving 0.0 or 30.1 mg of ractopamine HCl/kg DM.

Effects of various ractopamine hydrochloride withdrawal periods on performance, health, and carcass characteristics in yearling steers.

Ractopamine hydrochloride (RAC) is a β-adrenergic agonist approved for feeding during the last 28 to 42 d prior to cattle slaughter to improve feedlot performance and carcass characteristics. Three thousand crossbred yearling steers (527 ± 2.4 kg; AVG ± SD) were used in two periods to evaluate the effects of various RAC withdrawal times on feedlot performance, health, and carcass characteristics. In Period 1, 6 blocks of 30 pens totaling 1,500 steers were utilized, which was repeated for Period 2. In a randomized complete block design, cattle were assigned to 1 of 5 treatments consisting of 1) No RAC fed (CON), 2) 12-h RAC withdrawal (12-hRAC), 3) 2-d RAC withdrawal (2-dRAC), 4) 4-d RAC withdrawal (4-dRAC), and 5) 7-d RAC withdrawal (7-dRAC). Cattle were fed for a total of 62 d, and applicable treatments were supplemented with 30.0 ppm (dry matter basis) of RAC (average dose = 322 mg per steer per day) for 33 d at the end of the feeding period, corresponding to their respective withdrawal times. Initial body weight (BW) displayed a quadratic curve, with 2-dRAC and 4-dRAC withdrawal periods having the greatest BW. Accordingly, dry matter intake (DMI) responded quadratically (P = 0.034), with 2-dRAC and 4-dRAC treatments demonstrating the greatest DMI. No significant treatment differences (P ≥ 0.641) were observed in final live BW, average daily gain (ADG), or feed efficiency. Alternatively, when using a common dressing percentage to calculate live BW, cattle on RAC treatments exhibited 7.6 kg additional live BW (P < 0.001) compared to CON cattle. Furthermore, carcass-adjusted ADG and feed efficiency did not differ (P > 0.10) between RAC treatments but were improved compared to the CON treatment (P ≤ 0.002). Hot carcass weight (HCW) was on average 4.9 kg greater (P < 0.001) for RAC treatments vs. CON, and no differences were detected (P > 0.10) among RAC treatments. Within RAC treatments, carcass cutability responded quadratically (P ≤ 0.005) to withdrawal period, with the 2-dRAC and 4-dRAC treatments containing more Yield Grade 4 and 5 and fewer Yield Grade 1 and 2 carcasses than the other RAC treatments. On the basis of the results of this experiment, feeding RAC improves dressing percentage, HCW, and carcass-adjusted BW, ADG, and feed efficiency. Furthermore, extending the RAC withdrawal period to 7 d does not have a significant impact on cattle performance or health and has minimal effects on carcass characteristics.

Growth, performance, and carcass characteristics of feedlot Holstein steers fed ractopamine hydrochloride.

Growth-promoting technologies such as implants, ionophores, and β-agonists improve feedlot performance, efficiency, and carcass characteristics of cattle. The objective of this experiment was to determine the effects of dose and duration of ractopamine hydrochloride (RH) on feedlot performance and carcass characteristics when fed to Holstein steers. A randomized complete block design was used with a 3 × 3 factorial arrangement of treatments with 3 RH doses (0, 300, or 400 mg∙steer−1∙d−1) fed for 3 durations (28, 35, or 42 d). Holstein steers (n = 855; initial body weight [BW] = 448 ± 37 kg) were blocked by BW and randomly allocated to 1 of 9 pens (15 blocks; 9 dose × duration treatment combinations) approximately 72 d before harvest. Weekly pen weights, chute temperament scores, and animal mobility were determined during the RH feeding period. At harvest, carcass data were collected on all steers, and tenderness was measured on steaks from 3 or 4 randomly selected steers from each pen and slice shear force (SSF) was determined on one steak selected from each side of the carcass after aging for 14 or 21 d. For feedlot performance, carcass characteristics, and SSF, no dose × duration interactions were observed (P ≥ 0.11). With increasing RH dose, average daily gain (ADG) and gain-to-feed ratio (G:F) increased linearly (P ≤ 0.01), whereas BW gain increased linearly with RH dose and duration (P ≤ 0.01). Hot carcass weight (P = 0.02) and longissimus muscle (LM) area (P ≤ 0.01) increased linearly with increasing RH dose. The percentage of carcasses in the USDA Yield Grade 2 category increased linearly (P ≤ 0.01) and percentage of carcasses in the USDA Yield Grade 4 category tended (P = 0.08) to decrease linearly as RH dose increased. In the 14-d aged steaks, the percentage of steaks with SSF ≤ 15.3 kg decreased linearly (P ≤ 0.01), whereas the percentage of steaks with ≥20.0 kg SSF increased linearly (P ≤ 0.01) with increasing RH dose. After 21-d aging, there was a tendency (P = 0.06) for a greater percentage of steaks from steers fed RH to have SSF ≥ 20.0 kg (2% of total steaks), but no difference (P ≥ 0.12) in the percentage of steaks with SSF ≤ 19.9 kg. Final chute temperament (P ≥ 0.45) and animal mobility (P ≥ 0.67) scores were not affected by feeding RH. Increasing the dose of RH (300 or 400 mg∙steer−1∙d−1) fed for 28 to 42 d before harvest increased ADG, G:F, hot carcass weight, and LM area when fed to Holstein steers with no negative effects on behavior or mobility. The percentage of steaks classified as not tender improved when steaks were aged for 21 d from steers treated with RH.

Effects of increasing supplemental dietary Zn concentration on growth performance and carcass characteristics in finishing steers fed ractopamine hydrochloride.

Angus-cross steers (n = 288; 427 ± 0.4 kg) were utilized in a finishing study to evaluate the influence of increasing dietary Zn concentration on growth performance and carcass characteristics of steers fed ractopamine hydrochloride (RAC). In a randomized complete block design, steers were blocked by weight (6 steers/pen) and fed a dry-rolled corn-based diet for 79 d containing no supplemental Zn (CON; n = 8), 60 mg Zn/kg from ZnSO4 and no supplemental Zn-amino acid complex (ZnAA; ZnAA0; n = 8) or ZnAA0 diet supplemented with 60 (ZnAA60; n = 8), 90 (ZnAA90; n = 7), 120 (ZnAA120; n = 8), or 150 (ZnAA150; n = 8) mg Zn/kg DM from ZnAA. Thirty-one days prior to harvest (day 48 of study) all steers began receiving RAC at 300 mg⋅steer-1⋅d-1. This study was organized as 2 groups (GRP) of steers and groups were stagger started so that GRP1 started and ended 2 wk before GRP2. Pen was the experimental unit, and the statistical model included the fixed effects of treatment and block nested within GRP. Three a priori single degree of freedom contrasts were developed: linear and quadratic effects of ZnAA supplementation (ZnAA0, ZnAA60, ZnAA90, ZnAA120, and ZnAA150), and CON vs. Zn (CON vs. ZnAA0, ZnAA60, ZnAA90, ZnAA120, and ZnAA150). Dietary Zn concentration did not affect growth performance prior to RAC supplementation (P ≥ 0.17). During the RAC-period ADG and DMI were not affected by dietary Zn (P ≥ 0.16), while there was a linear effect of dietary Zn supplementation to decrease G:F (P = 0.04). Marbling scores were greatest in CON steers (P = 0.03). Liver Cu (day 45 and 80) and meat Cu (harvest) concentrations were greater in CON steers relative to Zn-supplemented steers (P ≤ 0.05), and plasma Zn linearly increased as dietary Zn increased (P = 0.007). Warner-Bratzler shear force was not different among treatments (P ≥ 0.25), and meat total collagen was quadratically affected by dietary Zn supplementation (P ≤ 0.002) where ZnAA0 was greatest. Overall, there was no effect of dietary Zn concentration on growth performance of RAC-supplemented steers in this study.

Ractopamine Hydrochloride Did Not Impact Carcass Traits, Muscle Fiber Types, or Sensory Traits of Long-Fed Yearling Heifers

Crossbred heifers (n = 64; animal was the experimental unit) were assigned to 1 of 8 treatments in a 4 × 2 factorial arrangement, with 4 treatment days-on-feed (DOF; 79, 100, 121, 142) and 2 levels of ractopamine hydrochloride (RAC) supplementation (0 or 300 mg × hd–1 × d–1). At 24 h postmortem, carcass traits were determined by trained personnel and longissimus samples were removed for muscle fiber type analyses. Boneless strip loins (IMPS #180) were fabricated and vacuum-packaged at 24 h postmortem and aged for 21 d, cut into 2.54 cm thick steaks, then frozen for no longer than 6 mo. After thawing for 24 h, Warner-Bratzler shear force (WBSF) and trained sensory panel analyses were conducted. Marbling was greater (P &lt; 0.05) for control (CON; 0 mg x hd-1 x d-1 ractopamine hydrochloride) heifers than RAC heifers fed for either 79 or 100 d, but lower (P &lt; 0.05) for CON heifers than RAC heifers fed for either 121 or 142 DOF. Feeding RAC had no effect (P &gt; 0.05) on carcass traits, muscle fiber histology, or meat quality. The addition of RAC had no effect (P &gt; 0.05) on Warner-Bratzler shear force. Feeding RAC had no negative impacts on carcass traits or meat quality and actually improved marbling scores in longer-fed heifers.

Effects of reducing dietary crude protein levels and replacement with crystalline amino acids on growth performance, carcass composition, and fresh pork quality of finishing pigs fed ractopamine hydrochloride.

Progeny of GPK-35 females mated to PIC 380 boars were blocked by initial BW, and within the 9 blocks, pens of pigs (3 gilts and 3 barrows/pen) were randomly assigned to dietary treatments where CP of finisher-I, -II, and -III diets was 1) 16.04, 14.55, and 16.23%, respectively (Ctrl); 2) 14.76, 13.48, and 15.27%, respectively (ILE); 3) 14.26, 12.78, and 14.28%, respectively (VAL); or 4) 12.65, 12.38, and 13.32%, respectively (NoSBM). All finisher-III diets included 10 mg/kg of ractopamine hydrochloride (RAC) and a Lys:ME ratio of 2.79 g/Mcal. At slaughter, HCW and Fat-O-Meat'er data were recorded before carcasses were subjected to a rapid chilling process. A subsample of whole hams (2/pen) and whole loins (2/pen) were transported under refrigeration to the University of Arkansas. Hams were dissected with a knife into lean, fat, and bone, and 2.5-cm-thick chops from the semimembranosus (SM) and the LM were used to measure fresh pork quality characteristics. Both ADG and G:F decreased (linear, = 0.05) as CP decreased in finisher-I diets, whereas ADFI was reduced (linear, = 0.01) in response to decreasing CP in finisher-II diets. When RAC was included in the finisher-III diets, ADFI and BW decreased (linear, ≤ 0.03) with decreasing CP, and pigs fed the ILE diet had greater (cubic, < 0.01) G:F than pigs fed the Ctrl and VAL diets. Across the entire finishing period, ADG and ADFI decreased (linear, = 0.01) in response to reductions in dietary CP. Conversely, reducing CP in finisher diets did not ( ≥ 0.13) affect carcass yield, fat depth, LM depth, or calculated fat-free lean yield, and dietary CP content did not ( ≥ 0.09) alter the lean, fat, or bone composition of fresh hams. Moreover, there was no effect of dietary CP on the visual and instrumental color or firmness of the LM ( ≥ 0.06) or SM ( ≥ 0.12). However, there were linear increases in LM marbling scores ( = 0.02) and intramuscular fat content ( = 0.03) as CP was reduced in the finisher diets. Although reducing dietary CP decreased overall ADG and ADFI by approximately 6.1 and 4.9%, respectively, carcass composition was not impacted by dietary CP level. More importantly, reducing dietary CP, although meeting the standard ileal digestible requirements for Lys, Thr, Trp, Met, Ile, and Val with crystalline AA, did not impact pork color or water-holding capacity and actually increased the intramuscular fat content of the LM.

Effects of ractopamine hydrochloride on the growth performance and carcass characteristics of heavy-weight finishing pigs sent for slaughter using a 3-phase marketing strategy.

A total of 2,158 crossbred pigs was used to evaluate the effects of feeding 7.4 mg/kg ractopamine hydrochloride (RAC) on the growth performance and carcass characteristics of heavy-weight finishing pigs sent to slaughter using a 3-phase marketing strategy. The study was performed from 121.0 ± 4.28 kg to 144.5 ± 4.73 BW using a randomized complete block design (blocking factor was d of start on test) with 2 treatments (0 vs. 7.4 mg/kg RAC). Pigs were housed in a commercial wean-to-finish facility in groups of approximately 25 (44 groups/treatment), with ad libitum access to feed and water throughout the study, and pen weights of pigs were recorded at the start (d 0), and on d 7, 21, and 35 of study. Pigs were sent for slaughter according to the following marketing strategy: 1) after 7 d on RAC, the heaviest 16% of each pen was sent for slaughter (Phase 1), 2) after 21 d on RAC, the next 40% of each pen was sent for slaughter (Phase 2), and 3) after 35 d on RAC, the remaining 44% of each pen was sent for slaughter (Phase 3). Pigs were selected for slaughter by visual appraisal and shipped to a commercial facility where standard carcass measurements (HCW, LM depth, and backfat depth) were measured. Overall, feeding RAC increased (P < 0.001) ADG (18.8%) and G:F (23.7%) compared to the control, but lowered (P < 0.001) ADFI (3.3%). In addition, feeding RAC increased (P < 0.001) HCW (3.9 kg), carcass yield (0.7% units), LM depth (5.0%), and predicted lean content (1.0% units), and reduced backfat depth (6.3% lower) compared to controls. With each subsequent phase of marketing, the magnitude of improvements in response to feeding RAC decreased for ADG (43.1, 20.9, and −3.1% for Phase 1, 2, and 3, respectively) and G:F (37.5, 25.8, and 6.4% for Phase 1, 2, and 3, respectively); however, improvements in HCW (1.6, 4.5, and 4.2 kg for Phase 1, 2, and 3, respectively), carcass yield (0.2, 0.6, and 0.9% units for Phase 1, 2, and 3, respectively), LM depth (2.3, 5.7, and 5.2% for Phase 1, 2, and 3, respectively), and predicted lean content (0.2, 1.0, and 1.3% units for Phase 1, 2, and 3, respectively) generally increased from feeding RAC. These results suggest that while improvements in growth performance from feeding RAC will generally decline after 21 d of feeding, improvements in carcass traits, particularly carcass yield and lean content, will continue with feeding RAC until d 35.

A3 Early Career Award Speaker: Interactions between trace minerals and growth promoting practices in beef cattle

Trace minerals (TM) are necessary to support optimum animal growth. While TM requirements to prevent deficiency were recently updated, the requirements of beef cattle to support optimal performance remain ill defined. Advancements in animal genetics and utilization of technologies to promote growth of feedlot cattle have dramatically advanced production efficiencies in the beef industry. Trace minerals (Co, Cu, Fe, I, Mn, Se and Zn) are integral in a variety of growth processes in the body, including supporting metalloproteins involved in DNA synthesis, collagen production, energy utilization and critical antioxidant enzymes. Over 80% of feedlot cattle are estimated to receive hormone implants to enhance growth and efficiency. Recently, we examined the effect of feeding no supplemental TM, TM supplemented at NRC recommendations, or TM supplemented at industry recommended concentrations (all inorganic sources), fed to Angus cross steers receiving no implant or implanted with Component TE-IS, followed by Component TE-200 on d 56. Harvested on d 124, HCW was, as expected, improved (P = 0.0001) by implant, but HCW was also improved by 15 kg (P = 0.01) in steers supplemented at industry TM concentrations vs. those receiving no supplemental TM. Additional work is needed to clarify the potentially greater need for TM in cattle receiving hormone implants. Introduction of beta adrenergic agonists revolutionized late stage finishing cattle performance, increasing feed efficiency, ADG, and often HCW of cattle. In a series of studies we have found that increasing supplementation of Zn (from a combination of inorganic and organic sources) to steers fed ractopamine hydrochloride increases cattle performance (ADG, feed efficiency, and HCW in some studies) during the ractopamine feeding period. Zinc is thought to inhibit breakdown of the intracellular signalling molecule, cAMP, perhaps potentiating the growth response. Alternately, demand for Zn and other TM may simply be greater due to increased growth rates. We recently found the retention of Zn and N to be positively correlated and that both ractopamine hydrochloride and Zn increase N retention in steers. It seems likely that growth enhancing technologies influence TM requirements of cattle, and further work is needed to determine TM requirements that optimize cattle performance and maximize producer profitability.

Effects of ractopamine hydrochloride on growth performance, carcass characteristics, and physiological response to different handling techniques.

Feedlot cattle ( = 128; BW = 549 ± 60 kg) were used to evaluate the effects of ractopamine hydrochloride (RAC) on growth performance, physiological response to handling, and mobility during shipment for slaughter in a study utilizing a split-plot design with a 2 × 2 factorial arrangement of treatments: 1) diet (CON [no β-adrenergic agonist] vs. RAC [400 mg·animal·d ractopamine hydrochloride for 28 d]) and 2) handling intensity (HI; low-stress handling [LSH; cattle moved at a walking pace with no electric prod use] vs. high-stress handling [HSH; cattle moved at a minimum of a trot and an electric prod applied while in the alley for posthandling restraint and during loading for shipment to the abattoir]). Cattle fed RAC tended to have greater ADG and G:F ( = 0.06), and had greater HCW and LM area ( = 0.04). The HI treatments were applied on the day after the 28-d growth performance period. Blood samples were collected before HI treatment (baseline), after HI treatments (POSTHAND), after transport to the abattoir (POSTTRANS), and during exsanguination at slaughter. A diet × HI interaction ( = 0.01) was observed in the change in cortisol from baseline to POSTTRANS, and there tended ( ≤ 0.07) to be diet × HI interactions for the change in epinephrine from baseline to POSTHAND and for the change in creatine kinase (CK) from baseline to POSTTRANS. Feeding RAC and HSH both increased the change from baseline to POSTHAND in norepinephrine and pH ( ≤ 0.05). The HSH cattle also had greater changes from baseline to POSTHAND in blood HCO, base excess, partial pressure of CO, lactate, cortisol, and glucose ( ≤ 0.01). Ractopamine and HSH both produced greater increases in CK concentrations from baseline to slaughter ( < 0.01). Mobility was not affected by RAC at the feedlot or following an average 6-h lairage ( ≥ 0.43). This study confirms RAC improves growth performance and suggests metabolic acidosis, a precursor to fatigued cattle syndrome, develops in cattle allowed to trot without the use of a lead rider regardless of RAC administration. Cattle fed RAC displayed altered hormonal responses to handling and transport stress, and the overall proportion of cattle with compromised mobility appears to increase later in the marketing channel. These findings warrant additional research aimed at better understanding the physiological response to stress and protect the welfare of cattle during shipment for slaughter.

Effect of handling intensity at the time of transport for slaughter on physiological response and carcass characteristics in beef cattle fed ractopamine hydrochloride.

The effects of handling intensity on the physiological response and carcass characteristics of feedlot cattle fed ractopamine hydrochloride were evaluated at the time of transport to slaughter. Eighty steers (BW = 668 ± 36 kg) representing 10 lots of similar breed, frame size, and degree of finish were blocked by lot, stratified by weight, and randomly assigned to 1 of 2 handling intensities (HI) over a 1,600 m dirt alley course: 1) low-stress handling (LSH) or 2) high-stress handling (HSH). For the LSH treatment, 4 penmates were kept at a walk with the use of a lead rider. For the HSH treatment, 4 penmates were kept at a minimum of a trot and received 2 applications of an electric prod (approximately 1 s per impulse) at 2 separate instances: first in the alley before post-handling sampling, and again during loading for transportation to the abattoir. Behavioral observations and physical indicators of stress were recorded a minimum of 1 h before handling (baseline), immediately after handling (POSTHAND), and while in lairage after a 200 km transport to the abattoir. Vital parameters were recorded at baseline and POSTHAND. Venous blood samples were collected via jugular venipuncture at baseline and POSTHAND, and mixed arterial and venous blood samples were collected during exsanguination at slaughter. Muscle tremors tended to be more prevalent in HSH cattle at POSTHAND ( = 0.10). The HSH cattle tended to have greater POSTHAND heart rate ( = 0.08); however, there was no effect of HI on POSTHAND respiration rate or rectal temperature ( 0.34). The HSH cattle had greater lactate, epinephrine, norepinephrine, cortisol, and glucose concentrations at POSTHAND ( ≤ 0.02). Additionally, HSH cattle had lower POSTHAND blood pH, bicarbonate, base excess, and partial pressure carbon dioxide ( < 0.0001). Bicarbonate concentrations were greater in HSH cattle at slaughter ( = 0.05); however, there were no differences between HI treatments for the remaining blood variables ( 0.11). Concentrations of stress hormones and CK were significantly greater at slaughter relative to baseline and POSTHAND for both LSH and HSH cattle ( < 0.001). These findings suggest cattle trotted without a lead rider develop metabolic acidosis, and illustrate the importance of low-stress handling at the time of transport for slaughter. Further research is warranted to develop strategies to mitigate stress at the time of transport and ensure the welfare of beef cattle presented to abattoirs.

Comparison of meat quality characteristics, growth, and feed efficiency of intact and castrated post-pubertal bovine males

Yearling Red Angus or Black Angus bulls (n = 24; initial BW = 1,336 ± 25.1 lb; (606 ± 11.4 kg); average 16 mo of age) were used to evaluate the effects of castration and use of growth promoting technology (STR) on performance, carcass traits, and meat quality characteristics when compared to intact (BULL) post-pubertal male cattle. The STR treatment included administration of a combination 120 mg trenbolone acetate + 24 mg estradiol growth-promoting implant on d 0 and feeding ractopamine hydrochloride the last 28 d on feed. Cattle were individually fed a corn-based finishing diet for 62 d and harvested at a commercial abattoir. Intact bulls had greater average daily gain (4.08 vs 3.19 lb or 1.85 vs 1.45 kg/d; P = 0.02) and feed:gain ratio (8.54 vs 10.97; P = 0.02) than STR. There were no treatment differences for dry-matter intake, quality or yield grade, hot carcass weight, back-fat thickness, or dressing percent (P &lt; 0.05). Longissimus muscle area was greater in BULL compared to STR carcasses (16.6 vs 15.0 in2 or 106.9 vs 96.8 cm2; P &lt; 0.01). Warner-Bratzler Shear Force was not affected (P &gt; 0.05) by treatment. Intact bulls had improved performance with no differences in carcass characteristics, tenderness, or sensory panel measurements compared to STR treatment.