Ractopamine at the Center of Decades-Long Scientific and Legal Disputes: A Lesson on Benefits, Safety Issues, and Conflicts

Ractopamine (RAC) is a synthetic phenethanolamine, β–adrenergic agonist used as a feed additive to develop leanness and increase feed conversion efficiency in different farm animals. While RAC has been authorized as a feed additive for pigs and cattle in a limited number of countries, a great majority of jurisdictions, including the European Union (EU), China, Russia, and Taiwan, have banned its use on safety grounds. RAC has been under long scientific and political discussion as a controversial antibiotic as a feed additive. Here, we will present significant information on RAC regarding its application, detection methods, conflicts, and legal divisions that play a major role in controversial deadlock and why this issue warrants the attention of scientists, agriculturists, environmentalists, and health advocates. In this review, we highlight the potential toxicities of RAC on aquatic animals to emphasize scientific evidence and reports on the potentially harmful effects of RAC on the aquatic environment and human health.

Transcriptome analyses indicate that heat stress-induced inflammation in white adipose tissue and oxidative stress in skeletal muscle is partially moderated by zilpaterol supplementation in beef cattle

Heat stress (HS) triggers oxidative stress, systemic inflammation, and disrupts growth efficiency of livestock. β-adrenergic agonists supplemented to ruminant livestock improve growth performance, increase skeletal muscle mass, and decrease carcass fat. The objective of this study was to understand the independent and interacting effects of HS and zilpaterol hydrochloride (ZH) supplementation on the transcriptome of subcutaneous white adipose tissue and the longissimus dorsi muscle in steers. Twenty-four Red Angus-based steers were assigned to thermoneutral (TN; Temperature Humidity Index [THI] = 68) or HS (THI = 73-85) conditions and were not supplemented or supplemented with ZH (8.33 mg/kg/d) for 21 d in a 2 × 2 factorial. Steers in the TN condition were pair-fed to the average daily feed intake of HS steers. RNA was isolated from adipose tissue and skeletal muscle samples collected via biopsy on 3, 10, and 21 d and sequenced using 3' Tag-Seq to an achieved average depth of 3.6 million reads/sample. Transcripts, mapped to ARS-UCD1.2, were quantified. Differential expression (DE) analyses were performed in DESeq2 with a significance threshold for false discovery rate of 0.05. In adipose, 4 loci (MISP3, APOL6, SLC25A4, and S100A12) were DE due to ZH on day 3, and 2 (RRAD, ALB) were DE due to the interaction of HS and ZH on day 10 (Padj < 0.05). In muscle, 40 loci (including TENM4 and OAZ1) were DE due to ZH on day 10, and 6 loci (HIF1A, LOC101903734, PDZD9, HNRNPU, MTUS1, and TMCO6) were DE due to environment on day 21 (Padj < 0.05). To explore biological pathways altered by environment, supplement, and their interaction, loci with DE (Praw < 0.05) were evaluated in Ingenuity Pathway Analysis. In adipose, 509 pathways were predicted to be altered (P < 0.01): 202 due to HS, 126 due to ZH, and 181 due to the interaction; these included inflammatory pathways predicted to be upregulated due to HS but downregulated due to the interaction of HS and ZH. In muscle, 113 pathways were predicted to be altered (P < 0.01): 23 due to HS, 66 due to ZH, and 24 due to the interaction of HS and ZH. Loci and pathway data in muscle suggest HS induced oxidative stress and that the stress response was moderated by ZH. Metabolic pathways were predicted to be altered due to HS, ZH, and their interaction in both tissues. These data provide evidence that HS and ZH interact to alter expression of genes in metabolic and immune function pathways and that ZH moderates some adverse effects of HS.

Growth, carcass characteristics, cut yields and meat quality of lambs finished with zilpaterol hydrochloride and steroid implant

Forty hairbreed male lambs were used to evaluate the effects of zilpaterol hydrochloride (ZH, 0 and 0.15 mg/kg BW) and steroid implant (SI, without and with 52.5 mg trenbolone acetate and 7.5 mg 17β-estradiol) on feedlot performance, carcass characteristics, non-carcass components, wholesale cut yield, and meat quality. Supplemental ZH increased growth rate, feed efficiency, carcass weight, and dressing percentage, with no effect on wholesale cut yields. Feeding ZH increased muscle pH at 24 h. Supplemental ZH increased meat shear force, but decreased lightness, redness, and yellowness after frozen storage followed by a 14-day aging period. The SI administration increased dressing percentage and neck yield, but decreased testicle weight and meat redness, without affecting other variables. The LT area was greater with ZH + SI administration than with individual application of ZH or SI. Compared to individual administration, simultaneous application of ZH and SI did not result in improved growth performance, carcass traits and wholesale cut yields in hairbreed male lambs.

Review: Effects of Ractopamine Hydrochloride (Paylean) on welfare indicators for market weight pigs

This review summarizes the effects of ractopamine hydrochloride (RAC) dose (5, 7.5, 10, and 20 mg/kg) on market weight pig welfare indicators. Ractopamine hydrochloride (trade name Paylean) is a β-adrenergic agonist that was initially approved in the U.S. in 1999 at doses of 5 to 20 mg/kg to improve feed efficiency and carcass leanness. However, anecdotal reports suggested that RAC increased the rate of non-ambulatory (fatigued and injured) pigs at U.S. packing plants. This led to the addition of a caution statement to the Paylean label, and a series of research studies investigating the effects of RAC on pig welfare. Early research indicated that: (1) regardless of RAC administration, fatigued (non-ambulatory, non-injured) pigs are in a state of metabolic acidosis; (2) aggressive handling increases stress responsiveness at 20 mg/kg RAC, while 5 mg/kg reduces stress responsiveness to aggressive handling. Given this information, dosage range for Paylean was changed in 2006 to 5 to 10 mg/kg in market weight pigs. Subsequent research on RAC demonstrated that: (1) RAC has minimal effects on mortality, lameness, and home pen behavior; (2) RAC fed pigs demonstrated inconsistent prevalence and intensity of aggressive behaviors; (3) RAC fed pigs may be more difficult to handle at doses above 5 mg/kg; and (4) RAC fed pigs may have increased stress responsiveness and higher rates of non-ambulatory pigs when subjected to aggressive handling, especially when 20 mg/kg of RAC is fed.

Effect of ractopamine hydrochloride (Optaflexx) dose and duration on growth performance and carcass characteristics of finishing steers

Three experiments evaluated the effects of ractopamine hydrochloride (RAC) dose and duration on growth performance and carcass characteristics of feedlot steers. In total, 1,509 crossbred steers (530 kg initial BW [SD 22]) were used in a randomized complete block design using a 3 × 3 factorial treatment structure. Treatments consisted of RAC dose (0, 100, or 200 mg/steer daily) and duration (28, 35, or 42 d) of RAC feeding prior to harvest. Initiation of RAC dose was staggered (7 d apart) based on RAC duration, which resulted in common days on feed among treatments. Data from the 3 experiments were combined for statistical analyses. There were no RAC dose × duration interactions ( ≥ 0.85) for growth performance. Live final BW was not different ( ≥ 0.24) as RAC dose increased. Dry matter intake linearly decreased ( < 0.01) as RAC dose increased. Live ADG and G:F linearly increased ( ≤ 0.01) as RAC dose increased. Carcass-adjusted ADG and G:F linearly increased ( ≤ 0.02) as RAC dose increased. Compared with steers fed 0 mg RAC/steer daily, G:F was improved by 5.0 and 13.0% when steers were fed 100 ( = 0.31) and 200 ( = 0.01) mg RAC/steer daily, respectively. Hot carcass weight tended ( = 0.10) to linearly increase as RAC dose increased, with carcasses from steers fed 100 ( = 0.38) and 200 ( = 0.10) mg RAC/steer daily being 2.2 and 4.1 kg heavier, respectively, than carcasses from steers fed 0 mg RAC/steer daily. Increasing RAC dose linearly ( < 0.01) increased LM area and linearly ( = 0.02) decreased marbling score. Live final BW was not different ( ≥ 0.60) among RAC durations. Carcass-adjusted final BW, ADG, and G:F were not different ( ≥ 0.41) as RAC duration increased. Carcass traits did not differ ( ≥ 0.18) among RAC duration. Feeding 200 mg RAC/steer daily improved ADG, feed efficiency, and HCW. Increasing the feeding duration of RAC had no effect of growth performance or carcass characteristics. These data indicate that feeding 200 mg RAC/steer daily for 28 d improves steer growth performance.

Urinary Excretion of the β-Adrenergic Feed Additives Ractopamine and Zilpaterol in Breast and Lung Cancer Patients

β₂-Adrenergic agonists (β-agonists) have been legally used in the U.S. for almost two decades to increase lean muscle mass in meat animals. Despite a cardiotoxic effect after high-dose exposure, there has been limited research on human β-agonist exposures related to meat consumption. We quantified urinary concentrations of ractopamine and zilpaterol, two FDA-approved β-agonist feed additives, and examined the extent to which the concentrations were associated with estimated usual meat intake levels. Overnight urine samples from 324 newly diagnosed breast cancer patients and spot urine samples from 46 lung cancer patients at the time of diagnosis, prior to treatment, were collected during 2006-2010 and 2014-2015, respectively. Urinary ractopamine and zilpaterol concentrations were measured by LC-MS/MS. Ractopamine and zilpaterol, respectively, were detected in 8.1% and 3.0% of the urine samples collected (n = 370). Only 1.1% (n = 4) of the urine samples had zilpaterol concentrations above the limit of quantification, with the mean value of 0.07 ng/mL in urine. The presence of detectable ractopamine and zilpaterol levels were not associated with meat consumption estimated from a food frequency questionnaire, including total meat (P = 0.13 and 0.74, respectively), total red meat (P = 0.72 and 0.74), unprocessed red meat (P = 0.74 and 0.73), processed red meat (P = 0.72 and 0.15), and poultry intake (P = 0.67 for ractopamine). Our data suggest that the amount of meat-related exposure of β-agonists was low.

Níveis de lisina digestível em dietas contendo ractopamina para suínos em terminação

Objetivou-se avaliar níveis de lisina digestível em dietas contendo 5 ppm de ractopamina sobre o desempenho e características quantitativas de carcaça de suínos em fase de terminação. Foram utilizados 96 suínos, sendo 48 machos castrados e 48 fêmeas, com peso inicial de 83,57 ± 4,07kg, distribuídos em delineamento inteiramente ao acaso, com quatro níveis de lisina digestível (0,94; 0,96; 1,02 e 1,04%), com três repetições de oito animais cada. O período experimental teve duração de 28 dias. O consumo de ração diário reduziu e a conversão alimentar melhorou linearmente de acordo com o aumento dos níveis de lisina digestível das dietas. Os pesos final, de frigorífico e de carcaça quente, o rendimento de carcaça, a quantidade de carne magra e o índice de bonificação aumentaram linearmente de acordo com o aumento dos níveis de lisina digestível. Não houve efeito dos níveis de lisina digestível sobre o ganho de peso diário, perda de peso durante o transporte e a porcentagem de carne magra da carcaça. Concluiu-se que, em dietas contendo 5ppm de ractopamina, o nível de 1,04% de lisina digestível melhora a conversão alimentar e aumenta o peso final, o peso e o rendimento de carcaça, a quantidade de carne magra e o índice de bonificação das carcaças dos suínos.

Effects of ovariectomization and ractopamine hydrochloride inclusion on heifer feedlot performance, meat yield, and tenderness of select muscles

Forty-eight British cross heifers were used to examine the effects of ovariectomization (OVX v. intact; INT) and ractopamine-HCl inclusion (0 or 0.41 mg/kg of BW day(-1); NORAC or RAC) for the final 31 days on performance, meat yield, and tenderness of select muscles. Ractopamine supplemented heifers had heavier BW (P≤0.05) and greater dressing percent than NORAC. Dressing percent was also greater (P<0.01) for INT v. OVX. LM area tended to be larger for RAC (P=0.07) and was larger for INT (P=0.05). Neither ractopamine inclusion nor sex class affected (P>0.08) organ weights or percent intramuscular fat. Ractopamine inclusion increased (P≤0.05) subprimal weight for the shoulder clod and bottom round. However, ractopamine inclusion and sex class had minimal effects on subprimal yields or slice shear force. Heifers receiving ractopamine had increased BW, DP, carcass weight and select subprimal weights without impacting meat quality. Ovariectomization did not influence the affects of ractopamine supplementation.

A long journey to effective obesity treatments: is there light at the end of the tunnel?

As the obesity epidemic continues, more Americans are getting fatter, having more weight-related problems such as cardiovascular disease, and are experiencing new metabolic dysfunctions. For over 50 years, the adipose tissue (AT), commonly referred to as fat, has been of interest to academic and clinical scientists, public health officials and individuals interested in body composition and image including much of the average public, athletes, parents, etc. On one hand, efforts to alter body shape, weight and body fat percentage still include bizarre and scientifically unfounded methods. On the other hand, significant new scientific strides have been made in understanding the growth, function and regulation of anatomical and systemic AT. Markers of transition/conversion of precursor cells that mature to form lipid assimilating adipocytes have been identified. Molecular 'master' regulators such as peroxisome proliferator-activated receptor gamma and CCAAT-enhancer-binding proteins were uncovered and regulatory mechanisms behind variables of adiposity defined and refined. Interventions including pharmaceutical compounds, surgical, psychosocial interventions have also been tested. Has all of the preceding research helped alleviate the adverse physiologies of overweight and/or obese people? Does research to date point to new modalities that should be the focus of efforts to rid the world of obesity-related problems in the 21st century? This review provides a general overview of scientific efforts to date and a provocative view of the future for adiposity.

Current recommended levels of dietary lysine in finisher pig diets are sufficient to maximise the response to ractopamine over 28 days but are insufficient in the first 7 days

Dietary ractopamine increases lean tissue deposition and responses increase as dose is increased provided sufficient dietary lysine is supplied. In Australia, diets supplemented with ractopamine (RAC) are formulated with 0.56 g available lysine per MJ digestible energy. The present study was conducted to investigate the interactions between dietary RAC and lysine on growth and carcass characteristics in ad libitum fed (13.8 MJ/kg) boars and gilts. The study involved 108 individually penned pigs at 17 weeks of age (64.1 ± 0.57 kg) in a 2 by 2 by 3 factorial design, with the respective factors being sex (gilt or boar), dietary lysine (low and high, i.e. 0.56 or 0.65 g available lysine/MJ digestible energy, respectively) and dietary RAC (0, 5 or 20 mg/kg) for 28 days. Over the 28-day study duration, both lysine diets containing dietary RAC were sufficient to elicit a response in average daily gain (ADG) (+5.8%, P = 0.026) and carcass weight (3%, P = 0.045), but not in feed efficiency (FE) (P = 0.555). However, over the period of the first 7 days, there were interactions between the effects of RAC and lysine for FE (P = 0.025) and ADG (P = 0.023), with both traits being responsive only to dietary RAC containing the high lysine, which increased FE (+9.1%, P = 0.002) and ADG (+7.2%, P = 0.068). Dietary RAC improved FE in the latter stages of the study, namely Days 15–21 (+5.7%, P = 0.031) and Days 22–28 (+4.9%, P = 0.040). The high RAC diet reduced carcass P2 backfat (–16.5%, P < 0.001) and fat tissue deposition (–6.2%, P = 0.074) and high lysine tended to reduce fat tissue deposition (–13.3%, P = 0.072). A sex by lysine interaction (P = 0.043) was observed for lean tissue deposition at 28 days, such that only the high-lysine diet increased lean deposition in boars (+11%, P < 0.05) but not in gilts. Dietary RAC tended to increase lean deposition (+14.0%, P = 0.067) in the first 14 days; however, only the high RAC diet increased lean deposition (+9.6%, P < 0.05) over 28 days. In conclusion, the current recommended supplementation levels of lysine for commercial gilts and boars fed RAC may limit the response to dietary RAC if the feeding regime is for short durations and boars will not maximise their lean tissue deposition rates.

Reduced age at slaughter in youthful beef cattle: Effects on carcass merit traits

López-Campos, Ó., Basarab, J. A., Baron, V. S., Aalhus, J. L. and Juárez, M. 2012. Reduced age at slaughter in youthful beef cattle: Effects on carcass merit traits. Can. J. Anim. Sci. 92: 449–463. Two-hundred and twenty-four spring-born British×Continental crossbred steers were used in a 2-yr project to evaluate the effect of production system (calf-fed vs. yearling-fed) and its interaction with breed cross and hormone implant strategies, with and without β-adrenergic agonist on carcass characteristics. Carcasses from yearling-fed steers were 32% heavier (P<0.001), resulting in higher (P<0.05) dressing percentages, grade fat and rib-eye (longissimus thoracis) area (REA) (1.1, 32 and 10%, respectively). However, despite being lighter, the estimated lean yield percentage was 3% greater (P=0.010) in carcasses from calf-fed steers. No difference (P>0.05) was observed for marbling scores between production systems. Use of hormonal implants increased (P<0.001) weights of live animals and carcasses (7 and 9%, respectively). However, non-implanted yearling-fed steers had the lowest proportion of Canada Quality Grade A and the highest proportion of Canada Quality Grade AAA carcasses (P<0.001). Moreover, the observed increase (P=0.016) in marbling scores (up to 37%) from British cross-bred steers disappeared with the use of implants. The only effect observed on carcass traits from the use of β-adrenergic agonists was an increase of 6% in REA (P=0.032). The main production system effect observed for carcass composition was a lower (P=0.008) proportion of bone in carcasses from yearling-fed steers. The use of hormonal implants increased (P<0.001) the proportion of lean and decreased (P=0.019) the proportion of fat (P<0.05). Overall carcass composition of steers with large Continental influence (>50%) had a higher proportion of lean and bone and a lower proportion of fat than carcasses from 50–75% British steers (P<0.001), which was also reflected in the composition of several individual primal cuts (e.g., rib, short-loin, flank, chuck and plate). The interactions amongst production systems and the other production factors studied were minimal. Therefore, despite expected differences in carcass size, reducing age at slaughter did not have a negative impact on Canadian beef carcass traits.

Ractopamina na dieta da carpa húngara (Cyprnus carpio) criada em tanques-rede

Avaliou-se a utilização da ractopamina como promotor de crescimento para carpa húngara em experimento com 56 dias de duração, realizado em 12 tanques-rede de pequeno volume, utilizando-se 360 peixes com peso inicial de 18,64±1,25g. Foram testadas três quantidades de ractopamina, 7, 14 e 21ppm/kg, mais a dieta controle. Avaliaram-se o peso médio, o comprimento total, a altura, a taxa de crescimento específico e o fator de condição. Foram também analisadas a composição corporal, a deposição tecidual e a glicose plasmática dos peixes. Não foi observado efeito significativo da adição de ractopamina sobre as características de desempenho. Observou-se maior concentração de glicose, 61,67mg/dL, nos peixes alimentados sem a adição de ractopamina na dieta. A adição de ractopamina na dieta proporcionou maior quantidade de gordura corporal nos peixes e não afetou a quantidade de proteína. Conclui-se que a adição de ractopamina na dieta não é eficiente para juvenis de carpa húngara.

Qualidade da carne de fêmeas suínas alimentadas com diferentes concentrações de ractopamina na dieta

Analisaram-se as qualidades física, química e sensorial, bem como o perfil de ácidos graxos da carne de fêmeas suínas alimentadas com dietas com concentrações crescentes de ractopamina. Foram utilizadas 468 fêmeas, com peso inicial de 84,77±7,20kg, alojadas em 36 baias e alimentadas com dietas contendo 0, 5, 10 ou 15mg de ractopamina/kg. Após o período de 28 dias, dois animais de cada baia, depois de passarem por 15 horas de jejum sólido, foram abatidos. Uma amostra do músculo Longissimus da meia carcaça direita foi colhida para se avaliar as características de qualidade da carne. Não houve efeito (P>0,05) da adição de ractopamina às dietas sobre o pH, capacidade de retenção de água, força de cisalhamento, cor e oxidação lipídica da carne. Observou-se efeito quadrático (P<0,05) para perdas por cocção da carne, e não foi observada diferença (P>0,05) na análise sensorial da carne. Também não foi observado efeito (P>0,05) sobre a composição em ácidos graxos e sobre a relação entre ácidos graxos saturados:insaturados. A adição de até 15mg de ractopamina/kg de dieta não altera as características físicas, sensoriais e o perfil de ácidos graxos da carne de fêmeas suínas abatidas com 110kg de peso.

Response to ractopamine-HCl in heifers is altered by implant strategy across days on feed1

Two experiments were conducted to investigate the effects of ractopamine-HCl (RAC) and implant strategy or days on feed (DOF) on feedlot performance and expression of beta-adrenergic receptors (AR). In Exp. 1, 1,147 feedlot heifers weighing 282 +/- 3 kg were used with implant treatments of Revalor-200 (R200) at arrival, or Revalor-IH at arrival with reimplantation with Finaplix-H on d 58 (RF). Ractopamine (0 vs. 200 mg/d) was fed the last 28 d in both experiments. Treatments were randomly assigned to 16 pens. At slaughter, semimembranosus muscle tissue was excised for RNA isolation. Ractopamine administration increased (P < 0.05) ADG, G:F, HCW, and LM; decreased (P < 0.05) 12th rib fat depth; and improved (P < 0.05) yield grade. There was no effect (P > 0.10) on the expression of beta1-AR mRNA; however, there was a tendency (P = 0.10) for RAC feeding to increase beta2-AR mRNA levels. For beta3-AR mRNA, there was an implant by RAC interaction (P = 0.05), with RAC numerically increasing beta3-AR mRNA in heifers implanted with RF, but a decrease (P < 0.05) in expression in heifers implanted with R200. Ractopamine also decreased (P < 0.05) IGF-I mRNA in heifers implanted with RF. In Exp. 2, 2,077 heifers were used to investigate the effects of RAC and DOF. Days on feed were 129, 150, and 170, and RAC was administered the last 28 d. Ractopamine improved (P < 0.05) G:F, but had no other effects (P > 0.05) on performance. Average daily gain decreased (P < 0.05) as DOF increased. Hot carcass weight, LM area, 12th rib fat, G:F, calculated yield grade, and marbling score increased (P < 0.05) and the percentage of KPH fat decreased (P < 0.05) as DOF increased. These data aid in our understanding of the effects of steroidal implants, DOF, and RAC administration in feedlot heifers.

Ractopamine induces differential gene expression in porcine skeletal muscles1

Ractopamine (RAC) improves growth by increasing lean accretion and decreasing fat deposition through repartitioning nutrients from adipose tissue to skeletal muscle. Although the process is not completely understood, RAC alters the proportion of muscle fiber type composition toward a faster-contracting phenotype. Because one of the primary determinants of contractile speed is the relative abundance of myosin heavy chain (MyHC) isoforms and because the genes encoding these isoforms are transcriptionally regulated, RAC likely alters MyHC gene expression. Using real-time PCR, the relative abundance of transcripts of individual type I, IIA, IIX, and IIB, and total MyHC, as well as glycogen synthase, citrate synthase, lactate dehydrogenase, peroxisome proliferator activated receptor alpha, beta1-adrenergic receptor (AR), and beta2-AR were determined in the LM of 44 pigs fed RAC (20 mg/kg) for 0, 1, 2, or 4 wk. In addition, MyHC isoform expression was determined in the LM and red semitendinosus and white semitendinosus muscles of 48 pigs fed RAC (20 mg/kg) for shorter periods of 12, 24, 48, or 96 h. Type I MyHC expression was unaffected (P > 0.73) by RAC administration. Type IIA MyHC expression decreased (P < 0.0001) by 96 h, was lower (P < 0.0001) by 1 wk, and returned to normal by 4 wk. Type IIX MyHC mRNA decreased (P < 0.001) by 2 wk and continued to decrease (P < 0.0001) by 4 wk. Most interesting was an increase (P < 0.0001) in type IIB MyHC by 12 h, which was maintained at an elevated level throughout the 4-wk feeding period. Abundance of glycogen synthase transcript was increased (P < 0.05) by 12 h, but was not different from controls at 2 wk, and was lower (P < 0.01) at 4 wk. Gene expression of beta1-AR was not affected by feeding RAC, whereas beta2-AR gene expression was decreased (P < 0.05) by 2 wk. These data show MyHC genes are differentially regulated by RAC and suggest that the beta adrenergic agonist-induced repartitioning effect is, in part, mediated by changing muscle fiber type-specific gene expression, perhaps through the beta2-AR.

Effects of ractopamine supplementation on behavior of British, Continental, and Brahman crossbred steers during routine handling

Equal numbers of British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 420) were used to examine the effects of ractopamine supplementation and biological type on behavior during routine handling. Steers were blocked by BW within type and allocated to pens, resulting in 2 pens (10 cattle per pen) representing each block x type subclass. Pens within each block x type subclass then were randomly assigned to ractopamine supplementation treatments (0 or 200 mg.steer(-1).d(-1)), which were administered during the final 28 d of the finishing period. At the time final BW were obtained (28 d after treatment initiation), a single, trained observer, blinded with respect to treatment designations, recorded subjective scores to characterize behavior of each animal. Scores included entry force score (degree of force required to load the animal into the chute); entry speed score (walk, trot, run); chute behavior score (calm, restless shifting, moderate struggling); and exit speed score (walk, trot, run). Ractopamine supplementation had no effect on entry force score, chute behavior score, or exit speed score; however, cattle supplemented with ractopamine entered the chute more rapidly than did control cattle. Biological cattle type was a significant source of variation in entry force score and exit speed score. Continental crossbreds required greater (P < 0.05) force to enter the squeeze chute than did Brahman crossbred or British steers. In addition, Continental crossbred and Brahman crossbred steers left the processing chute with the greatest speed, whereas British steers exited the processing chute most slowly. Biological cattle type did not affect scores for entry speed or behavior during restraint in the chute. No adverse effects of ractopamine supplementation on cattle behavior were observed in this study.

The rainbow trout skeletal muscle beta-adrenergic system: characterization and signaling

The presence and functionality of beta-adrenoceptors (beta-ARs) were examined in red (RM) and white muscle (WM) membranes isolated from the rainbow trout Oncorhynchus mykiss. Specific binding assays revealed the presence of a single class of binding sites with similar affinities in both muscle types (K(d) in nM: 0.14 +/- 0.03 and 0.18 +/- 0.03 for RM and WM, respectively) but with a significantly higher number of binding sites in RM compared with WM (B(max) in fmol/mg protein: 3.22 +/- 0.11 and 2.60 +/- 0.13, respectively). Selective and nonselective beta-adrenergic agonists (beta-AAs) and antagonists indicated an atypical beta-AR pharmacology. This result may represent a nonmammalian beta-AR classification or, more likely, the presence of more than one beta-AR subtype in trout muscles with similar affinities that could not be kinetically resolved. Adenylyl cyclase (ACase) assays showed a dose-dependent increase in cAMP production as concentrations of beta(2)-AAs increased in both muscle membranes with significantly higher basal cAMP production in RM compared with WM (cAMP production in pmol cAMP. mg protein(-1). 10 min(-1): 24.67 +/- 3.06 and 9.64 +/- 3.45, respectively). The agonist-induced increase in cAMP production was blocked by the beta-adrenergic antagonist propranolol, while the ACase activator forskolin increased cAMP production by 7- to 14-fold above basal and approximately 3-fold above all beta-AAs tested. This study demonstrated the presence of atypical beta(2)-ARs on RM and WM membranes of trout, suggesting that beta(2)-AAs may be a tool to enhance protein accretion through this signaling pathway.