Zilpaterol Hydrochloride Research Articles

Feedlot performance and carcass traits of hairbreed ewe lambs in response to zilpaterol hydrochloride and soybean oil supplementation.

The aim of the present study was to evaluate the impact of zilpaterol hydrochloride (ZH; 0 or 10 mg/lamb daily) and soybean oil (SBO; 0 or 6%) supplementation on feedlot performance, carcass traits, and wholesale cut yield of 32 Dorper × Pelibuey ewe lambs (30.55 ± 2. 57 kg of initial BW). Lambs were blocked by BW and randomly assigned to treatments under a randomized complete block design with a 2 × 2 factorial arrangement. After a 34-d feeding period, all ewes were slaughtered. No ZH × SBO interactions were detected (P ≥ 0.11) for the variables evaluated. In the overall feeding period and first 17 d of experiment, feedlot performance was not affected (P ≥ 0.26) by ZH supplementation, but from d 18 to 34, ZH increased (P ≤ 0.03) total gain, ADG, and G:F without affecting DMI (P = 0.58). Also, ZH increased (P ≤ 0.02) HCW, cold carcass weight, dressing percentage, LM area, and leg perimeter. Lung weight as percentage of final BW decreased (P = 0.05) whereas other noncarcass components and wholesale cut yields were not affected (P ≥ 0.06) by ZH supplementation. Inclusion of SBO did not affect (P ≥ 0.08) feedlot performance or wholesale cut yields. The LM pH at 24 h postmortem as well as liver and peritoneum percentages were decreased (P ≤ 0.05) by SBO supplementation, but no other carcass characteristics or noncarcass components were affected (P ≥ 0.08) by SBO. In conclusion, feedlot performance and carcass characteristics were not altered by the interaction of ZH × SBO. However, ZH alone increased the growth of ewes during the last 17 d of the feeding period. Likewise, carcass characteristics of economic importance (i.e., HCW, dressing percentage, LM area, and leg perimeter) increased with ZH supplementation. In general, feedlot performance, carcass traits, and wholesale cut yields were not altered by including 6% of SBO in the finishing diet of ewe lambs.

Impact of sorting before feeding zilpaterol hydrochloride on feedlot performance and carcass characteristics of yearling steers.

Two studies evaluated sorting and feeding zilpaterol hydrochloride (ZH) on feedlot performance and carcass characteristics in randomized block-designed finishing trials. In Exp. 1 (initial BW 342 ± 10 kg, = 1,000), 5 treatments included an unsorted non-ZH fed negative control (-CON), an unsorted ZH fed positive control (+CON), and 3 treatments in which the heaviest 20% within the pen were sorted and marketed 28 d early and the remaining 80% were fed ZH. The 20% were identified at the beginning (EARLY), 100 d from slaughter (MIDDLE), or 50 d from slaughter (LATE). Because of sorting, the remaining steers in sorted treatments were fed 14 d longer than -CON and +CON. Average days on feed for control treatments were 165 and 173 d for the EARLY, MIDDLE, and LATE treatments. In Exp. 2 (initial BW 376 ± 29 kg, = 1,400), 4 treatments included -CON; +CON; an early weight sort fed ZH (1-SORT) with the heaviest 20% identified at d 1 and sorted 50 d from harvest and marketed 14 d before -CON and +CON, with the remaining 80% of the pen fed 7 d longer than -CON and +CON; and a 4-way sort 50 d from harvest fed ZH (4-SORT) with steers sorted into HEAVY, MID-HEAVY, MID-LIGHT, and LIGHT groups marketed -14, 0, +7, and +28 d from -CON and +CON, respectively. Average days on feed for control treatments were 154 and 157 d for the 1-SORT and 159 d for 4-SORT. Steers were fed Zilmax at 8.3 mg/kg DM for 20 d followed by a 3 d withdrawal. In Exp. 1, steers fed +CON had 13 kg greater (P < 0.01) HCW than steers fed -CON. Steers sorted EARLY, MIDDLE, and LATE had 28, 25, and 24 kg heavier ( P< 0.01) HCW than -CON steers, respectively. Carcass weight SD was greater (P = 0.01) for +CON than -CON but was not different (P = 0.17) between -CON and ZH sorted treatments. Percentage of overweight carcasses (454 kg) was greater (P ≤ 0.05) in sorted treatments than in -CON. In Exp. 2, HCW for +CON was 15 kg heavier (P < 0.01) than that for -CON, and HCW for 4-SORT was greater (P < 0.02) than that for +CON. Carcass weight SD was not different (P > 0.10) between +CON and -CON, whereas carcass weight SD of 4-SORT was reduced (P < 0.01) compared with that of -CON and +CON. Steers fed ZH had a greater percentage of carcasses over 454 kg than steers fed -CON (P < 0.01). Although not statistically different (P = 0.27), the percentage of carcasses over 454 kg was reduced by 28% for 4-SORT compared with +CON. Feeding ZH increases carcass weight, but sorting reduces variation, allowing further increases in carcass weight while minimizing overweight carcasses.

Effects of zilpaterol hydrochloride on growth performance, blood metabolites, and fatty acid profiles of plasma and adipose tissue in finishing steers1

The effects of zilpaterol hydrochloride (ZH) on blood metabolites and fatty acid profiles of plasma and adipose tissue were evaluated in crossbred finishing steers (n = 18, BW 639 ± 12.69 kg) that were stratified by BW and randomly assigned, within strata (block), to receive 0 (control) or 8.33 mg/kg diet DM ZH. Cattle were fed once daily ad libitum in individual feeding pens (9 pens/treatment). Zilpaterol hydrochloride was fed for 23 d and withdrawn 3 d before harvest. Blood samples and measures of BW were taken on d 0, 7, 14, and 21. Concentrations of β-hydroxybutyrate (BHB), glucose, and lactate were determined from whole blood. Nonesterified fatty acids, urea nitrogen (PUN), glucose, lactate, and long-chain fatty acid (LCFA) concentrations were analyzed from plasma. Postharvest, adipose tissue samples (approximately 20 g) from subcutaneous fat covering the lumbar vertebrae were collected after 48 h of refrigeration and analyzed for LCFA profiles. Feeding ZH decreased DMI by 8% (P = 0.03) but did not affect BW gain or efficiency (P = 0.83 and P = 0.56, respectively). Addition of ZH resulted in greater HCW, dressing percentage, and LM area ( P = 0.02, P = 0.08, and P = 0.07, respectively) but did not influence other carcass traits (P > 0.10). A ZH × d interaction was observed for PUN and whole-blood glucose concentrations (P = 0.06), in which concentrations decreased in cattle receiving ZH. Nonesterified fatty acids, BHB, plasma glucose, whole-blood, and plasma lactate concentrations were unaffected by ZH (P > 0.10). Zilpaterol hydrochloride increased plasma concentrations of elaidic (P = 0.03), vaccenic (P = 0.006), and docosapentaenoic acids ( P= 0.08), but LCFA concentrations of adipose tissue were unaffected ( P> 0.10), suggesting no preferential oxidation of specific fatty acids. In conclusion, ZH supplementation decreased PUN concentration possibly due to decreased muscle catabolism, but components of blood related to lipid oxidation were unaffected.

Effect of zilpaterol hydrochloride on animal performance and carcass characteristics in sheep: a meta-analysis

The present study constitutes a meta-analysis of the use of zilpaterol hydrochloride (ZH) in sheep production (18 studies, n = 724 animals were evaluated), focused in its effects on productive performance and carcass characteristics in sheep who were given ZH in different doses (control 0, ≤0.50 and ≥0.54 mg/kg raised to the power 0.75 body weight (BW)). The analysis of the data assembled in the database was conducted by a statistical meta-analysis based on mixed model methodology. Results on weight gain were higher (P < 0.03) for the group supplemented with ≥0.54 mg vs. control treatment, feed conversion improved (P < 0.01) with the inclusion of ZH compared with the control group. Carcass yield and Longissimus dorsi area showed no differences (P > 0.05) between treatments, fat content in the carcass diminished in a linear effect (P = 0.02) with the inclusion of ZH. The results show a positive effect on improving animal performance, mainly in the characteristics on the fat deposition. The optimal dose varies depending on the variable to improve, ranged in 0.24 up to 1.21 mg ZH/kg BW0.75 to reduce fat and carcass get leaner or increase average daily gain, respectively.

Influence of dietary zilpaterol hydrochloride on feedlot performance, carcass traits, chemical composition of longissimus muscle, and plasma metabolites of castrated male goats

To evaluate the influence of zilpaterol hydrochloride (ZH) supplementation on growth performance, carcass traits, chemical characteristics of the longissimus muscle (LM), and plasma metabolites, 16 Mahabadi castrated goats (29.93 ± 1.84 kg) were individually fed a finishing diet without or with ZH supplementation dosed at 0.20 mg/kg BW daily. Zilpaterol was fed for 30 days with 3 days of withdrawal before harvest. Compared with the controls, ZH supplementation decreased dry matter intake and increased total weight gain, average daily gain, and gain for feed. Hot carcass weight, dressing percentage, and LM area were increased, but back fat thickness and kidney-pelvic fat were reduced in the group that received ZH. Supplemental ZH did not affect the full viscera mass or stomach complex, but it increased empty body weight (EBW) and reduced (as g/kg final EBW) the heart/lungs and kidney weights. Zilpaterol supplementation increased LM protein and moisture and decreased LM fat. The goats fed with ZH had lower serum concentrations of glucose, triglycerides, and cholesterol than the controls. It can be concluded that daily ZH supplementation at 0.20 mg/kg BW increases growth performance, feed efficiency, and dressing percentage in castrated goats as a result of greater muscle accretion and causes reduction of fat and visceral organ mass

The effects of technology use in feedlot production systems on feedlot performance and carcass characteristics.

The objectives of this study were to examine the effects of feedlot production systems with and without the use of a β-adrenergic agonist compared to an all-natural production program on feedlot performance and carcass characteristics. Crossbred beef steers ( = 336; initial BW = 379 ± 8 kg) were randomized to 1 of 3 treatments in a randomized complete block design (RCBD; 14 steers/pen; 8 pens/treatment). Treatments consisted of an all-natural treatment (NAT), a conventional treatment (CONV), and a conventional treatment with a β-agonist (CONV-Z). All treatments were fed the same basal diet with NAT cattle receiving no growth promoting technologies. The CONV and CONV-Z cattle were implanted with 40 mg of estradiol and 200 mg of trenbolone acetate (TBA) on d 0 and were fed 33 and 9 mg/kg of monensin and tylosin daily, respectively. The CONV-Z cattle were fed zilpaterol hydrochloride (ZH) at 6.76 mg/kg (90% DM basis) for the last 20 days on feed (DOF) There was no effect of treatment on DMI ( = 0.83); however, CONV-Z steers gained 3.8% faster (1.64 vs. 1.58 kg/d; < 0.01) and were 5.3% more efficient (0.160 vs. 0.152; < 0.01) than CONV steers, and CONV steers gained 32.8% faster (1.58 vs. 1.19 kg/d; < 0.01) and were 26.7% more efficient (0.152 vs. 0.120; < 0.01) than NAT steers. There was a 35.7% improvement in estimated carcass gain (1.29 vs. 0.95 kg/d; < 0.01) and a 32.6% improvement in carcass efficiency (0.126 vs. 0.095; < 0.01) for CONV-Z steers compared to NAT steers. Hot carcass weight was increased by 8 kg for CONV-Z steers compared to CONV steers (394 vs. 386 kg; = 0.05) and 46 kg compared to NAT steers (394 vs. 348 kg; < 0.01). Longissimus muscle area was increased by 3.6 cm for CONV-Z steers compared to CONV steers (92.29 vs. 88.67 cm; = 0.02) and 12.1 cm for CONV-Z steers compared to NAT steers (92.29 vs. 80.16 cm; < 0.01), resulting in a 9.6% unit increase in USDA yield grade (YG) 1 (15.14 vs. 5.52%; < 0.05) and a 21.6% unit reduction in USDA YG 3 for CONV-Z steers compared to CONV steers (30.70 vs. 52.32%; < 0.05). The CONV-Z steers had a lower marbling score compared to the other treatments (432; 0.01), resulting in an 11.7% unit increase (20.70 vs. 9.03%; < 0.05) in USDA Select carcasses compared to CONV steers. The results of this experiment show that CONV-Z and CONV production results in a significant improvement in feedlot performance and USDA YG compared to NAT.

A meta-analysis of zilpaterol and ractopamine effects on feedlot performance, carcass traits and shear strength of meat in cattle.

This study is a meta-analysis of the effects of the beta-agonists zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RAC) on feedlot performance, carcase characteristics of cattle and Warner Bratzler shear force (WBSF) of muscles. It was conducted to evaluate the effect of the use of these agents on beef production and meat quality and to provide data that would be useful in considerations on the effect of these agents on meat quality in Meat Standards Australia evaluations. We conducted a comprehensive literature search and study assessment using PubMed, Google Scholar, ScienceDirect, Scirus, and CAB and identification of other studies from reference lists in papers and searches. Searches were based on the key words: zilpaterol, zilmax, ractopamine, optaflexx, cattle and beef. Studies from theses obtained were included. Data were extracted from more than 50 comparisons for both agents and analysed using meta-analysis and meta-regression. Both agents markedly increased weight gain, hot carcase weight and longissimus muscle area and increased the efficiency of gain:feed. These effects were particularly large for ZH, however, fat thickness was decreased by ZH, but not RAC. Zilpaterol also markedly increased WBSF by 1.2 standard deviations and more than 0.8 kg, while RAC increased WBSF by 0.43 standard deviations and 0.2 kg. There is evidence in the ZH studies, in particular, of profound re-partitioning of nutrients from fat to protein depots. This work has provided critically needed information on the effects of ZH and RAC on production, efficiency and meat quality.

Comparative effects of supplementing beef steers with zilpaterol hydrochloride, ractopamine hydrochloride, or no beta-agonist on strip loin composition, shear force, and consumer assessment of steaks aged for 14 or 21 d postmortem

Comparative effects of supplementing beef steers with zilpaterol hydrochloride, ractopamine hydrochloride, or no beta-agonist on strip loin composition, shear force, and consumer assessment of steaks aged for 14 or 21 d postmortem

Effect of ractopamine hydrochloride and zilpaterol hydrochloride on tenderness of Longissimus steaks of Bos taurus steers

Effect of ractopamine hydrochloride and zilpaterol hydrochloride on tenderness of Longissimus steaks of Bos taurus steers

Estimation of carcass composition using rib dissection of calf-fed Holstein steers supplemented with zilpaterol hydrochloride

Estimation of carcass composition using rib dissection of calf-fed Holstein steers supplemented with zilpaterol hydrochloride

Zinc methionine alters muscle cross-sectional area and fiber type of Holstein steers fed zilpaterol hydrochloride

Zinc methionine alters muscle cross-sectional area and fiber type of Holstein steers fed zilpaterol hydrochloride

Effects of beef production system on animal performance and carcass characteristics.

The objective of this study was to evaluate conventional (CONV) and natural (NAT) beef production systems from annual pasture through finishing through grazing. Beef steers (n=180, initial BW=250±19 kg) were assigned randomly to 2 treatments in the pasture phase. Steers were implanted with 40 mg of trenbolone acetate (TBA), 8 mg estradiol, and 29 mg tylosin tartrate (CONV), or received no implant (NAT). Steers on the 2 treatments grazed wheat or cereal rye for 109 d. Conventional steers had an 18.5% improvement in ADG (1.22 vs. 1.03 kg/d, P<0.01) and a heavier final BW (385 vs. 366 kg, P<0.01) compared with NAT steers. Following the pasture phase, steers (n=160 steers, 5 steers/pen, 8 pens/treatment) were assigned to a 2×2 factorial in the feedlot phase. Production system (NAT vs. CONV) was maintained from the pasture phase, and the second factor was 7 vs. 12% low-quality roughage (DM basis, LOW vs. HIGH). During finishing, CONV steers were given 120 mg of TBA and 24 mg estradiol at processing, fed monensin and tylosin, and fed zilpaterol hydrochloride for the last 20 d of the experiment. There were no program×roughage level interactions (P>0.07). The CONV steers ate 6.9% more feed (11.8 vs. 11.0 kg/d, P<0.01), gained 28.4% faster (1.90 vs. 1.48 kg/d, P<0.01), and were 24.2% more efficient (0.164 vs. 0.132, P<0.01) compared with NAT steers. The LOW steers had greater G:F (0.153 vs. 0.144, P<0.01) compared with HIGH steers. There was a 28.3% improvement in estimated carcass weight gain (1.36 vs. 1.06 kg/d), 18.6% improvement in carcass efficiency (0.115 vs. 0.097, P<0.01), and 21.6% improvement (1.52 vs. 1.25 Mcal/kg, P<0.01) in calculated dietary NEg for CONV compared with NAT steers. Hot carcass weight was increased by 62 kg (424 vs. 362 kg, P<0.01) and LM area was increased by 16.9 cm2 (100.9 vs. 84.0 cm2, P<0.01), decreasing USDA yield grade (YG, 3.09 vs. 3.54, P<0.01) for CONV steers compared with NAT steers. Natural steers had a greater percentage of carcasses in the upper 2/3 of USDA Choice grade (48.7 vs. 18.7%, P<0.01), a greater percentage of YG 4 and 5 carcasses (25.4 vs. 9.3%, P<0.01), and a greater percentage of abscessed livers (39.6 vs. 10.5%, P<0.01) compared with CONV steers. The results show that CONV production results in more rapid and efficient production that resulted in heavier carcasses with superior YG and desirable quality grades with both roughage levels.

Effects of growth-promoting technology on feedlot cattle behavior in the 21 days before slaughter

There is growing interest in the animal welfare implications of growth-promoting technology used in feedlot cattle, namely hormonal implants, ionophores, antibiotics and β2-adrenergic agonists. Previous studies have focused on the effects of implants on aggression, but little work has evaluated other behavioral changes anecdotally reported with β2-adrenergic agonists, such as an increase in lateral lying, a posture seen when cattle rest. The objectives of the present experiment were to quantify the effects of these technologies on lying and agonistic behavior in the 21 days before slaughter and to examine the sampling strategy required to measure lateral lying. Angus crossbred steers were assigned to 16 pens of 10 animals each. Treatments were applied in an additive manner to represent the decisions that feedlot managers would likely make about technology use. They were: (1) control (CON; no technology application), (2) monensin and tylosin phosphate (MON), (3) MON and growth implant (trenbolone acetate and estradiol, IMP) and (4) IMP and zilpaterol hydrochloride, a β2-adrenergic agonist (fed day 24–3 before slaughter; BAA). Agonistic (pushing, displacements) and bulling behaviors were recorded on day 21, 17, 12, 7 and 3 before slaughter and lying behavior, including time and number of bouts of lateral and sternal lying, was measured on day 12, 7, and 3. These time points were chosen to overlap with the feeding period for zilpaterol. BAA cattle spent 31% more time lying laterally, compared to all other treatments (BAA: 2.4 vs. others: 1.7h/24h, SE: 0.18h/24h, P=0.020), perhaps because of changes associated with muscle growth. Continuous measurement is needed to measure lateral lying; estimates generated with instantaneous scan sampling never met all of our criteria for accuracy (R2>0.9, slope=1, intercept=0). BAA cattle engaged in more pushing and displacements than MON or CON (P≤0.05); IMP also increased pushing compared to MON or CON, but only during day 12, 7 and 3 before slaughter (IMP and BAA 12.5pushes/steer/h vs. MON and CON 6.8pushes/steer/h, SE 1.4pushes/steer/h, P=0.007). Together, these findings indicate that combined use of growth-promoting technologies tested in this experiment affected both agonistic and lying behavior.

Beta agonists in livestock feed: status, health concerns, and international trade.

Since the U.S. Food and Drug Administration approved ractopamine hydrochloride and zilpaterol hydrochloride in animal feeds, usage of those compounds has been a topic of worldwide debate. Ractopamine and zilpaterol are β-adrenergic agonists used as veterinary drugs to increase weight gain in certain animals raised for food. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) established maximum residue limits for ractopamine, which were adopted by the Codex Alimentarius Commission (Codex). No maximum residue limits for zilpaterol have been adopted by JECFA, and new reports of animal mobility issues confront the use of this feed additive. However, many countries disagree with the Codex standards and are restricting or banning meat products containing β agonists. The bans by major importers of U.S. meat products have prompted some to advocate that the United States use the World Trade Organization dispute settlement body. This paper looks at the developments to provide a fuller accounting of what the issues may mean to U.S. firms selling meat products containing residues of β agonists.

Effects of feeding dry-rolled corn-based diets with and without wet distillers grains with solubles and zilpaterol hydrochloride on performance, carcass characteristics, and heat stress in finishing beef steers.

Zilpaterol hydrochloride (ZH) has been approved for use since 2006; however, there is no research on any interactions between ZH and coproducts. Additionally, there is no published information on the potential effects of ZH on heat stress in feedlot cattle. Therefore, an experiment was conducted to determine the effects of feeding dry-rolled corn (DRC)-based diets with and without wet distillers grains with solubles (WDGS) and ZH on performance, carcass characteristics, and heat stress in feedlot cattle. Four hundred thirty-eight steers were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments in 16 pens with 26 to 28 steers in each pen. Factors consisted of inclusion of 0 or 30% (on a DM basis) WDGS and inclusion of ZH at 0 or 84 mg/steer daily for 21 d at the end of the finishing period. Therefore, cattle were blocked by BW and randomly assigned to 1 of the resulting 4 treatment combinations: 1) DRC-based diet with 0% WDGS and 84 mg/steer ZH, 2) DRC-based diet with 0% WDGS and no ZH, 3) DRC-based diet with 30% WDGS and 84 mg/steer of ZH, and 4) DRC-based diet with 30% WDGS and no ZH. Final live BW, carcass-adjusted BW, ADG, and G:F were greater for cattle fed ZH than non-ZH-fed cattle (P < 0.01). Additionally, cattle fed ZH consumed 7.4% less DM than cattle not fed ZH (P < 0.01). Cattle fed ZH for 21 d also had a 2.9% greater HCW (P < 0.01), a 1.1% greater dressing percentage (P < 0.01), 7.3% greater LM area (P < 0.01), and an 8.4% improvement in yield grade (P < 0.01) than cattle not fed ZH. For the main effect of WDGS inclusion, ADG was greater for cattle fed 0 vs. 30% WDGS (P = 0.04) and G:F also tended to be greater for cattle fed 0 vs. 30% WDGS (P = 0.07) for the 21-d ZH feeding period. However, when evaluated over the entire experiment, cattle fed 30 vs. 0% WDGS had a greater ADG and G:F (P < 0.01). Furthermore, cattle fed 30 vs. 0% WDGS had a greater dressing percentage and tended to have a greater amount of 12th rib fat (P < 0.07). Heat stress measurements were collected during the time cattle were fed ZH, from May 31 to July 12, 2013. The slopes for change in respiration rate and panting score per day were positive but were not different across dietary treatments (P > 0.71); in addition, the slopes for change in respiration rate and panting score when accounting for environmental conditions were positive but were not different across dietary treatments (P > 0.32).

Biological responses of beef steers to steroidal implants and zilpaterol hydrochloride.

British × Continental steers (n = 168; 7 pens/treatment; initial BW = 362 kg) were used to evaluate the effect of dose/payout pattern of trenbolone acetate (TBA) and estradiol-17β (E2) and feeding of zilpaterol hydrochloride (ZH) on serum urea-N (SUN), NEFA, IGF-I, and E2 concentrations and LM mRNA expression of the estrogen (ER), androgen (ANR), IGF-I (IGF-IR), β1-adrenergic (β1-AR), and β2-adrenergic (β2-AR) receptors and IGF-I. A randomized complete block design was used with a 3 × 2 factorial arrangement of treatments. Main effects were implant (no implant [NI], Revalor-S [REV-S; 120 mg TBA + 24 mg E2], and Revalor-XS [REV-X; 200 mg TBA + 40 mg E2]) and ZH (0 or 8.3 mg/kg of DM for 20 d with a 3-d withdrawal). Steers were fed for 153 or 174 d. Blood was collected (2 steers/pen) at d -1, 2, 6, 13, 27, 55, 83, 111, and 131 relative to implanting; LM biopsies (1 steer/pen) were collected at d -1, 27, 55, and 111. Blood and LM samples were collected at d -1, 11, and 19 relative to ZH feeding. A greater dose of TBA + E2 in combination with ZH increased ADG and HCW in an additive manner, suggesting a different mechanism of action for ZH and steroidal implants. Implanting decreased (P < 0.05) SUN from d 2 through 131. Feeding ZH decreased (P < 0.05) SUN. Serum NEFA concentrations were not affected by implants (P = 0.44). There was a day × ZH interaction (P = 0.06) for NEFA; ZH steers had increased (P < 0.01) NEFA concentrations at d 11 of ZH feeding. Serum E2 was greater (P < 0.05) for implanted steers by d 27. Serum trenbolone-17β was greater (P < 0.05) for implanted steers by d 2 followed by a typical biphasic release rate, with a secondary peak at d 111 for REV-X (P < 0.05) implanted steers. Implanting did not affect mRNA expression of the ANR or ER, but the IGF-IR and the β1-AR and β2-AR were less (P < 0.05) for REV-S than NI at d 55 and β2-AR mRNA was less (P < 0.05) for REV-S than for REV-X. Expression of the IGF-IR and the β1-AR at d 111 was greater (P< 0.05) for REV-X than for REV-S and NI at d 111, and the β2-AR was less (P< 0.05) for REV-S than for REV-X. Feeding ZH did not affect mRNA expression of the β1-AR and β2-AR. Both implanting and feeding ZH decreased SUN, but a greater dose of TBA + E2 did not result in further decreases. In addition, feeding ZH increased serum NEFA concentrations. Metabolic changes resulting from implanting and feeding ZH may aid in explaining steer performance and carcass responses to these growth promotants.

Comparative effects of supplementing beef steers with zilpaterol hydrochloride, ractopamine hydrochloride, or no beta agonist on strip loin composition, raw and cooked color properties, shear force, and consumer assessment of steaks aged for fourteen or twenty-one days postmortem.

Beef steers (n = 1,914) were assigned to 1 of 3 β-adrenergic agonist (βAA) supplementation treatments-zilpaterol hydrochloride (ZH; 8.3 mg/kg of DM for 20 d with 3-d withdrawal), ractopamine hydrochloride (RH; 308 mg·head(-1)·d(-1) for 28 d), or no βAA (CON)-to determine the effects on consumer eating quality. Strip loins (n = 1,101; CON = 400, RH = 355, and ZH = 346) were obtained and fabricated into 2.5-cm-thick steaks for proximate, Warner-Bratzler shear force (WBSF), slice shear force (SSF), and consumer analyses; steaks were aged until 14 or 21 d postmortem. Fat and moisture contents were not affected by βAA supplementation (P > 0.05), but strip steaks from steers fed ZH had more protein (P < 0.01) than those from steers fed CON or RH, which were similar. An interaction between βAA and aging was observed (P < 0.01) for WBSF but not SSF. Within steaks aged 14 d, ZH steaks required the most force to shear, RH steaks were intermediate, and CON steaks had the lowest WBSF values; however, RH steaks had a stronger response to aging than CON or ZH steaks, resulting in the lowest WBSF values at 21 d. Slice shear force values were greater (P < 0.01) in steaks from steers fed ZH than in steaks from steers fed CON or RH, which did not differ. Following shear force analyses, steaks within 2 SD of each treatment mean for WBSF were selected randomly for consumer assessment of eating quality. Consumer testing (n = 400; 200/postmortem aging period) was arranged in a 3 × 3 factorial representing 3 quality grades (Select, Low Choice, and Premium Choice) and 3 treatments (ZH, RH, and CON). In steaks aged 14 d, βAA supplementation affected (P < 0.01) tenderness, flavor, and overall liking and tenderness acceptability, resulting in lower consumer scores for ZH than CON and RH; however, juiciness, flavor, and overall acceptability were similar (P > 0.05). In steaks aged 21 d, feeding βAA influenced (P < 0.01) only tenderness and juiciness scores. Despite these differences, βAA did not affect (P > 0.05) acceptability. Quality grade impacted (P < 0.01) all traits and acceptability in steaks aged 14 and 21 d. In 14-d steaks, Premium Choice typically was scored higher than Low Choice or Select; however, consumers rated 21-d Low Choice and Premium Choice similarly-both receiving greater scores than Select. Consumers detected several differences in eating quality at 14 d because of βAA supplementation. Increasing aging from 14 to 21 d mitigated differences in shear force and tenderness scores because of feeding ZH, so that tenderness and overall acceptability were similar between ZH, RH, and CON.

Effect of Zilpaterol Hydrochloride on Feedlot Performance and Carcass Characteristics in Weaner Steers

Effect of Zilpaterol Hydrochloride on Feedlot Performance and Carcass Characteristics in Weaner Steers

Increased Mortality in Groups of Cattle Administered the β-Adrenergic Agonists Ractopamine Hydrochloride and Zilpaterol Hydrochloride

The United States Food and Drug Administration (FDA) approved two β-adrenergic agonists (βAA) for in-feed administration to cattle fed in confinement for human consumption. Anecdotal reports have generated concern that administration of βAA might be associated with an increased incidence of cattle deaths. Our objectives, therefore, were to a) quantify the association between βAA administration and mortality in feedlot cattle, and b) explore those variables that may confound or modify this association. Three datasets were acquired for analysis: one included information from randomized and controlled clinical trials of the βAA ractopamine hydrochloride, while the other two were observational data on zilpaterol hydrochloride administration to large numbers of cattle housed, fed, and cared for using routine commercial production practices in the U.S. Various population and time at-risk models were developed to explore potential βAA relationships with mortality, as well as the extent of confounding and effect modification. Measures of effect were relatively consistent across datasets and models in that the cumulative risk and incidence rate of death was 75 to 90% greater in animals administered the βAA compared to contemporaneous controls. During the exposure period, 40 to 50% of deaths among groups administered the βAA were attributed to administration of the drug. None of the available covariates meaningfully confounded the relationship between βAA and increased mortality. Only month of slaughter, presumably a proxy for climate, consistently modified the effect in that the biological association was generally greatest during the warmer months of the year. While death is a rare event in feedlot cattle, the data reported herein provide compelling evidence that mortality is nevertheless increased in response to administration of FDA-approved βAA and represents a heretofore unquantified adverse drug event.

The effect of dietary energy and the inclusion of a β-adrenergic agonist in the diet on the meat quality of feedlot lambs

β-adrenergic agonists are commonly used in livestock production to enhance meat production and decrease the fat content of the body. β-adrenergic agonists normally improve growth performance. Recent increases in meat prices and the change in consumer preference towards leaner meat have resulted in more lamb producers opting to finish leaner mutton/lamb on farms in a feedlot system. The aim of this trial was to determine the effect of dietary energy, as well as the inclusion of a β-antagonist, on the meat quality of feedlot lambs. South African Mutton Merino lambs (108) of different sexes (rams and ewes) were weaned at 120 days of age and were randomly divided into six groups (18 lambs per group). The treatment consisted of three different dietary energy levels (high 12.7 MJ ME/kg feed, medium 12.0 MJ ME/kg feed and low 11.3 MJ ME/kg feed) with either the inclusion of a β-adrenergic agonist (zilpaterol hydrochloride) at 8.4 g/ton or not. Data were analysed according to a 3 (dietary energy) x 2 (inclusion of a stimulant) x 2 (sex) factorial analysis. No interaction occurred between treatments and the data were presented as the effect of dietary energy level, the inclusion of a stimulant and sex on proximate components, fat thickness and the tenderness of the meat. The factors β-adrenergic agonists and dietary energy level had no effect on the proximate components, fat thickness or the tenderness of the meat. The ewe lambs’ 9-11th rib-cut had a significantly higher fat content than the ram lambs (27.9% vs. 23.1%, respectively). Meat from ram lambs was less tender (63.60N) compared to that from ewe lambs (57.82N). Neither the inclusion of the β-adrenergic agonist (59.8N vs. 61.9N) nor the dietary energy level (59.3N vs. 63.5N vs. 59.3N) had an effect on the tenderness of meat from lambs in this study.Keywords: Meat quality, β-agonist, energy, South African Mutton Merino