Ractopamine Treatment Research Articles

Ractopamine at legal residue dosage accelerates atherosclerosis by inducing endothelial dysfunction and promoting macrophage foam cell formation

Ractopamine, a synthetic β-adrenoreceptor agonist, is used as an animal feed additive to increase food conversion efficiency and accelerate lean mass accretion in farmed animals. The U.S. Food and Drug Administration claimed that ingesting products containing ractopamine residues at legal dosages might not cause short-term harm to human health. However, the effect of ractopamine on chronic inflammatory diseases and atherosclerosis is unclear. Therefore, we investigated the effects of ractopamine on atherosclerosis and its action mechanism in apolipoprotein E-null (apoe−/−) mice and human endothelial cells (ECs) and macrophages. Daily treatment with ractopamine for four weeks increased the body weight and the weight of brown adipose tissues and gastrocnemius muscles. However, it decreased the weight of white adipose tissues in apoe−/− mice. Additionally, ractopamine exacerbated hyperlipidemia and systemic inflammation, deregulated aortic cholesterol metabolism and inflammation, and accelerated atherosclerosis. In ECs, ractopamine treatment induced endothelial dysfunction and increased monocyte adhesion and transmigration across ECs. In macrophages, ractopamine dysregulated cholesterol metabolism by increasing oxidized low-density lipoprotein (oxLDL) internalization and decreasing reverse cholesterol transporters, increasing oxLDL-induced lipid accumulation. Collectively, our findings revealed that ractopamine induces EC dysfunction and deregulated cholesterol metabolism of macrophages, which ultimately accelerates atherosclerosis progression.

Ractopamine hydrochloride induces behavioral alterations and oxidative status imbalance in zebrafish

ABSTRACTThe occurrence of ractopamine (RAC) hydrochloride in water bodies is of significant concern due to its ecological impacts and toxicity to humans. RAC hydrochloride is a β-adrenergic agonist drug used as a feed additive to (1) improve feed efficiency, (2) rate of weight gain, and (3) increase carcass leanness in animals raised for their meat. This drug is excreted by animals in urine and introduced into the environment affecting nontarget organisms including fish. In wastewater released from farms, RAC concentrations were detected from 0.124 µg/L to 30.1 µg/L, and in levels ranging from 1.3 × 10−5 to 5.4 × 10−4 μg/L in watersheds. The aim of this study was to examine the effects of exposure to RAC at 0.1, 0.2, 0.85, 8.5, or 85 µg/L dissolved in water on behavior and oxidative status in adult zebrafish. At 0.85 µg/L, RAC treatment increased exploratory behavior of zebrafish; while at 8.5 µg/L, decreased locomotor and exploratory activities were noted. With respect to oxidative stress biomarkers, results showed that RAC at 0.2 µg/L induced lipid peroxidation and elevated total thiol content in zebrafish brain. All drug tested concentrations produced a fall in nonprotein thiol content. Finally, RAC at 0.85, 8.5, or 85 µg/L increased catalase enzyme activity. Our results demonstrated that the exposure to RAC induced behavioral alterations and oxidative stress in zebrafish.

Rapid evaporative ionisation mass spectrometry and chemometrics for high-throughput screening of growth promoters in meat producing animals

ABSTRACTIn a proof of concept perspective, Rapid Evaporative Ionisation Mass Spectrometry (REIMS) was explored for the direct analysis of meat samples from β-agonist treated livestock. In this context, the combination of REIMS with untargeted metabolomics was investigated to identify carcasses from treated animals on the basis of a modification of indirect metabolites profile. The REIMS analysis generated specific lipid profiles which enabled the differentiation of meat samples collected from pigs treated with ractopamine via their feeding regime. Furthermore, the strategy was found successful when tested on different muscle types (loin, shoulder and thigh), which further expands its applicability. Classification performances were greater than 95% accurate which fully answers requirements of a screening strategy. This research indicates that REIMS implemented in an untargeted-metabolomics workflow can be considered as a high-throughput and accurate strategy for real-time meat classification in relation to ractopamine (and wider β-agonists) treatment in pig production. This approach may subsequently be implemented as a rapid screening test, at the slaughterhouse or at border inspection points, to detect such practice.

Expressions of matrix metalloproteinases and their inhibitor are modified by beta-adrenergic agonist Ractopamine in skeletal fibroblasts and myoblasts

Cha, M. C. and Purslow, P. P. 2012. Expressions of matrix metalloproteinases and their inhibitor are modified by beta-adrenergic agonist Ractopamine in skeletal fibroblasts and myoblasts. Can. J. Anim. Sci. 92: 159–166. The beta-adrenergic agonist ractopamine is known to promote growth and improve feed efficiency in animal production, in part by suppressing muscle protein degradation. This investigation aims to determine whether ractopamine modifies the expression of enzymes principally involved in intramuscular connective tissue turnover, the matrix metalloproteinases (MMPs) and their inhibitors, in the principal cell types of skeletal muscle. Mouse skeletal muscle fibroblasts (NOR-10 cells) and myoblasts (C2C12 cells) were cultured with or without 2 or 10 µM ractopamine for 6 or 24 h. Cellular MMP-2 expression was increased (P<0.05) by ractopamine in both cell lines. Cellular MMP-3 expression was also increased in response to ractopamine in myoblasts (P<0.03). The amount of a tissue inhibitor of MMPs (TIMP-1) in cell lysates of both cell lines was increased (P<0.05) by the 6-h ractopamine treatment. The extracellular expression of MMP-2 and TIMP-1 was increased (P<0.05) in myoblasts, but not in fibroblasts. The elevated TIMP-1 expression in medium is in the order of three times higher (P<0.02) than the increased activity of MMP-2 expressed by myoblasts at 6 h. In summary, ractopamine treatment results in a higher cellular expression of MMP-2 and MMP-3 as compared with the expression of their inhibitor TIMP-1. However, the increased extracellular MMP-2 activity is counterbalanced by the increased presence of TIMP-1. The findings show that ractopamine has the potential to alter connective tissue turnover in treated animals.

Physiopathological changes related to the use of ractopamine in swine: Clinical and pathological investigations

The aim of the study was to investigate clinical and pathological modifications induced by treatment with different doses of the β2-agonist ractopamine (RAC) in pigs. Thirty-two eight-month-old Landrace×Large White pigs (mean weight, 102.8±6.7kg) were treated with 0, 10 (R10), 20 (R20) and 40 (R40) mg/kg/diet of RAC for the last 35days before slaughtering. Before and after treatment body weight was recorded, blood samples were collected for complete blood count and thyroid hormone concentration analysis, and cardiac instrumental evaluation was performed. At slaughtering, tissue samples were collected for histopathological examination. None of the animals showed any signs of clinical disease during the study period. Treatment did not induce any statistically significant difference in complete blood counts (P>0.05) among groups. A significant (P<0.05) decrease in feed consumption was observed between R10 and R40 treated animals. A significant (P<0.01) increase in ventricular internal dimensions and left ventricular mass was observed in R20; a significant reduction in thyroid weight (P<0.05) was observed in the animals receiving the highest-dose treatment (R40). Urethral hyperplasia and metaplasia, and prostate hyperplasia and a significant (P<0.05) reduction in circulating triiodothyronine levels were found in overall treated animals. Taken together, these data suggest that RAC treatment in pigs induces adaptative non-neoplastic urethral and prostatic disorders of growth and a reduction in thyroid hormone concentrations. Nevertheless, additional research on a larger group of animals is needed to define the biomolecular mechanisms underlying the observed lesions, in order to improve the surveillance tools to identify illegal treatments.

Effects of a “step-up” ractopamine feeding program, sex, and social rank on growth performance, hoof lesions, and Enterobacteriaceae shedding in finishing pigs1

Increasing concern for animal well-being and food safety has stimulated the investigation of feed additives such as ractopamine (RAC), a beta-agonist widely used to improve production performance of finishing pigs. The objective of this study was to determine effects of RAC feeding, delivered as a "step-up" program (5 mg/kg for 2 wk followed by 10 mg/kg for 2 wk), on growth performance, Enterobacteriaceae shedding, including Salmonella, and hoof lesions, also taking into account sex and social rank of pigs. A total of 64 barrows and gilts (balanced by treatment and sex) were assigned to pens of 4 (by sex) as either control (CTL) or RAC treatment. Social ranks (dominant, intermediate, and subordinate) of pigs in each pen were determined by behavioral observation during 48 h post-mixing. Fecal samples were collected once per week for 5 wk. At slaughter, the 32 dominant and subordinate barrows and gilts (16/sex) were examined for hoof lesions, and luminal contents from ileum, cecum, and rectum were collected. Pigs fed RAC had increased growth performance (P < 0.05) with social rank of animals affecting overall ADG (P < 0.05). Gilts gained more backfat than barrows when comparing to baseline values at both 10th and last ribs (P < 0.05), whereas loin eye area increased at a similar rate for both barrows and gilts (P > 0.10). No significant effect of RAC feeding was found on backfat or loin eye area (P > 0.10). At slaughter, RAC-fed pigs had greater BW (P < 0.05). Despite the positive effects of RAC feeding on growth performance, pigs fed the compound had a greater frequency of front and rear hoof lesions as did barrows and dominant individuals (P < 0.05). Detectable concentrations of Salmonella shedding were not identified at any time during the experiment. Enterobacteriaceae shedding concentrations from RAC-fed pigs peaked at the first week of feeding and progressively decreased until slaughter. At slaughter, rectal and cecal Enterobacteriaceae concentrations were less in RAC-fed pigs than in CTL pigs (P < 0.05). Social rank tended to affect gut Enterobacteriaceae populations of barrows more than in gilts (P < 0.10). The effects of RAC feeding on hoof soundness and Enterobacteriaceae populations in the gastrointestinal tract of finishing pigs warrant further investigation. It is also proposed that the integration of the social rank status of the individual into future studies should be considered, because it may affect treatment responses.

Effect of Ractopamine HCl Supplementation on Fecal Shedding of Escherichia coli O157:H7 and Salmonella in Feedlot Cattle

The effects of the beta-agonist ractopamine, recently approved for use in feedlot cattle to improve carcass quality and performance, on fecal shedding Escherichia coli O157:H7 and Salmonella in feedlot cattle was examined. In the first study, 20 feedlot steers and heifers were randomly assigned to receive ractopamine or no ractopamine (control) by way of oral bolus for 28 days. Fecal samples were collected daily, and shedding of E. coli O157:H7 determined. When examined during the entire 28-day experimental period, ractopamine decreased (P = 0.0006) the percentage of cattle shedding E. coli O157:H7 (58% vs. 42% for control and ractopamine treatments, respectively). A second study was conducted in a commercial feedlot facility in the southwestern United States. Eighteen pens of cross-bred beef heifers (approximately 100 head/pen and 9 pens/treatment) were randomly assigned to receive either 0 (control) or 200 mg ractopamine/head x d(-1). Fresh fecal samples (30/pen) were collected off the pen floor before ractopamine supplementation and again after approximately 28 days of ractopamine supplementation (within a few days of slaughter); the samples were cultured for E. coli O157:H7 and Salmonella. The percentage of animals shedding E. coli O157:H7 was decreased when data were pooled across replicates (P = 0.05) in ractopamine-treated cattle compared with controls. The percentage of animals shedding Salmonella tended to be higher (P = 0.08) with the ractopamine treatment when data were pooled across replicates. Although further research is required to confirm these results, the potential food safety implications of this research are intriguing.

The effect of feeding ractopamine (Paylean) on muscle quality and sensory characteristics in three diverse genetic lines of swine.

The present experiment utilized Berkshire (n = 76), Duroc (n = 81), and high-lean commercial crossbred (n = 75) barrows and gilts with an initial BW of approximately 85.1 kg. Pigs were fed a standard commercial diet (17.6% CP, 1.02% lysine) supplemented with ractopamine hydrochloride at a level of 0 or 10 ppm for 28 d. The experiment was conducted in a randomized complete block design, with animals blocked within genetic line according to litter, gender, and weight, for a total of four blocks per genetic line for each treatment. Pigs were harvested at a commercial abattoir and chilled for 24 h at 1 to 4 degrees C. At 24 h postmortem, wetness and firmness scores and ultimate muscle pH were measured in the center of the longissimus muscle (LM) at the 10th to 11th rib interface. Visual and instrumental color and marbling score were measured at 48 h postmortem on a fresh cut LM surface. Percentage of chemically extracted intramuscular fat (IMF) was measured, and a trained sensory panel evaluated cooked LM chops for juiciness, tenderness, and chewiness. Cooking loss (%) and instrumental measurement of tenderness also were measured on cooked LM chops. Ractopamine treatment increased ADG (P < 0.01) and LM area (P < 0.05), but had no effect (P > 0.05) on LM quality, sensory attributes, or instrumental measures of palatability. Berkshire LM received higher tenderness and juiciness (P < 0.05) scores and had lower cooking losses (P < 0.05) and instrumental tenderness (P < 0.05) than LM from the Duroc and high-lean lines. Loins from barrows were firmer (P < 0.05), had lower drip loss percentages (P < 0.05), and received greater tenderness scores (P < 0.05) than the LM from gilts. Genetic line x treatment and gender x treatment interactions were detected for IMF. The LM of Berkshire pigs fed ractopamine had lower (P < 0.05) IMF than Berkshires fed the control diet, with no interaction in the other lines. Purebred barrows (Berkshire and Duroc) had greater (P < 0.001 and P < 0.05, respectively) IMF than their respective purebred gilts, with no gender difference in IMF in the high-lean line. Results from the present study indicate that feeding ractopamine does not affect most muscle quality and palatability characteristics. However, the genetic line x treatment interaction for loin IMF suggests that feeding ractopamine might reduce IMF within the loin muscle of genetic lines that have a propensity to produce greater levels of IMF.

Ractopamine treatment biases in the prediction of pork carcass composition.

Carcass and live measurements of 45 barrows were used to evaluate the magnitude of ractopamine (RAC) treatment prediction biases for measures of carcass composition. Barrows (body weight = 69.6 kg) were allotted by weight to three dietary treatments and fed to an average body weight of 114 kg. Treatments were: 1) 16% crude protein, 0.82% lysine control diet (CON); 2) control diet + 20 ppm RAC (RAC16); 3) a phase feeding sequence with 20 ppm RAC (RAC-P) consisting of 18% crude protein (1.08% lysine) during wk 1 and 4, 20% crude protein (1.22% lysine) during wk 2 and 3, 16% crude protein (0.94% lysine) during wk 6, and 16% crude protein (0.82% lysine) during wk 6. The four lean cuts from the right side of the carcasses (n = 15/treatment) were dissected into lean and fat tissue. The other cut soft tissue was collected from the jowl, ribs, and belly. Proximate analyses were completed on these three tissue pools and a sample of fat tissue from the other cut soft tissue. Prediction equations were developed for each of five measures of carcass composition: fat-free lean, lipid-free soft tissue, dissected lean in the four lean cuts, total carcass fat tissue, and soft-tissue lipid mass. Ractopamine treatment biases were found for equations in which midline backfat, ribbed carcass, and live ultrasonic measures were used as single technology sets of measurements. Prediction equations from live or carcass measurements underpredicted the lean mass of the RAC-P pigs and underpredicted the lean mass of the CON pigs. Only 20 to 50% of the true difference in fat-free lean mass or lipid-free soft-tissue mass between the control pigs and pigs fed RAC was predicted from equations including standard carcass measurements. The soft-tissue lipid and total carcass fat mass of RAC-P pigs was overpredicted from the carcass and live ultrasound measurements. Prediction equations including standard carcass measurements with dissected ham lean alone or with dissected loin lean reduced the residual standard deviation and magnitude of biases for the three measures of carcass leanmass. Prediction equations including the percentage of lipid of the other cut soft tissue improved residual standard deviation and reduced the magnitude of biases for total carcass fat mass and soft-tissue lipid. Prediction equations for easily obtained carcass or live ultrasound measures will only partially predict the true effect of RAC to increase carcass leanness. Accurate prediction of the carcass composition of RAC-fed pigs requires some partial dissection, chemical analysis, or alternative technologies.

Change in Insulin Sensitivity or Responsiveness Is Not a Major Component of the Mechanism of Action of Ractopamine in Beef Steers

Our objective was to determine whether the β-adrenergic agonist ractopamine altered sensitivity or responsiveness to insulin. We used the hyperinsulinemic, euglycemic clamp approach in five multicatheterized beef steers to evaluate insulin sensitivity (ED50) and responsiveness (Rmax or Rmin) during control or ractopamine feeding (80 mg/kg feed). Steers had blood vessel catheters and ultrasound flow probes that allowed measurement of net uptake and release of glucose and insulin by portal-drained viscera (PDV), liver and hindlimb. Steers ate meals of equal size every 2 h. Steers were fed at 1.8 times calculated maintenance energy. The design was a single reversal. Two rates of insulin infusion followed a base-line period on each of three sample days. Insulin was infused into a mesenteric vein at 10, 20, 40, 80, 160 and 320 mU/(h⋅kg body weight). During the base-line period, arterial concentrations of glucose, oxygen, nonesterified fatty acids and insulin were not different between control and ractopamine feeding. Arterial urea was lower during ractopamine than during control feeding (5.02 vs. 6.20 mmol/L, respectively, P < 0.01). Net release of glucose by liver and net uptake of glucose by the hindlimb were not affected by treatment. Similarly, net release of insulin by PDV and net uptake of insulin by liver were not affected by treatment. The Rmax and ED50 for steady-state glucose infusion rate, total glucose entry, hepatic glucose production and hindlimb glucose uptake did not differ between treatments. There was a trend for a lower ED50 in hindlimb with ractopamine treatment (P < 0.13). These data do not support a change in sensitivity or responsiveness of tissues to insulin as a major component of the mechanism of action of ractopamine.

Lipolytic responses to catecholamines in ractopamine-treated pigs

The β-agonist ractopamine (RAC) promotes protein deposition with little effect on fat deposition in the pig. To assess whether the lack of effect on fat deposition was due to changes in response to catecholamines, crossbred pigs with venous catheters were used to examine plasma non-esterified fatty acid (NEFA) concentrations before and after intravenous (i.v.) injections of the (β1+β2)-agonist isoproterenol and the β2-agonist fenoterol during dietary RAC (0 or 20 mg/kg) treatment. In Expt 1, gilts received increasing i.v. doses of fenoterol [3, 9, 27, 81, and 243 µg/kg bodyweight (BW)] on Day 34 and blood samples were taken for metabolite analyses. The protocol was repeated on Day 36 but this time using increasing doses of isoproterenol (0·11, 0·33, 1, 3, and 9 µg/kg BW). Dietary RAC decreased basal NEFA concentrations but had no effect on plasma glucose concentrations. When the individual NEFA responses to fenoterol curves were fitted, the derived values for maximal response (Rmax) suggested that there was no difference between pigs fed 0 or 20 mg/kg RAC (1739 v. 1847 µmol/L, P = 0 ·829). However, there was an almost 10-fold increase in the dose of fenoterol required to elicit a NEFA response 50% of Rmax (ED50) in RAC-fed pigs (11·6 v. 107·0 µg/kg, P = 0·008). Intravenous fenoterol challenge increased plasma glucose linearly but this response was not altered by dietary RAC. In Expt 2, gilts received increasing i.v. doses of fenoterol (16, 80, and 400 µg/kg BW) on Day 10 and blood samples were taken for metabolite analyses. The protocol was repeated on Day 11 but this time using increasing doses of isoproterenol (6·25, 32·5, and 162·5 mg/kg BW). The derived values for Rmax suggested that there was no effect of injected β-agonist (2209 v. 2405 µmol/L for fenoterol and isoproterenol, respectively, P = 0·204) or dietary RAC (2251 v. 2363 µmol/L for 0 or 20 mg/kg RAC, respectively, P = 0·448) on Rmax. However, the ED50 was significantly lower for isoproterenol than for fenoterol (14·1 v. 31·3mg/kg, P = 0·001) and was increased by dietary RAC (18·6 v 26·9 µg/kg, P = 0·05). In conclusion, these data support the hypothesis that the lack of effect of dietary RAC on the rate of lipid deposition in the pig is due to a desensitisation of adipose tissue β-adrenergic receptors with no change in adipose tissue responsiveness.

Ractopamine increases glucose turnover without affecting lipogenesis in the pig

The β-agonist ractopamine (RAC) promotes protein deposition with little effect on fat deposition in the pig. The present study was conducted to assess whether the lack of effect on fat deposition was due to a lack of effect of ractopamine on lipogenesis. Twenty crossbred pigs (initial liveweight 80 kg) surgically prepared with cephalic vein catheters were used in a 2×2 factorial experiment with the respective factors being sex (boar or gilt) and dietary RAC (0 or 20 mg/kg of ractopamine.HCl). Pigs were offered 3·0 kg/day of their respective diets for 24 days. On Day 4 and 23 of the experiment, pigs were injected with [U- 14C]-glucose and serial blood samples taken to determine glucose turnover. Adipose tissue biopsies were taken 240 min after injection of labelled glucose and lipogenesis was estimated from the incorporation of 14C into adipose tissue lipid. Dietary RAC increased average daily gain (P &lt; 0·050), and average growth rate was greater in boars than in gilts (P &lt; 0·050). Dietary RAC increased glucose turnover by 24%, presumably to support the increased skeletal muscle protein deposition that occurs during dietary RAC treatment. There was no effect of dietary RAC on the rate of lipogenesis in adipose tissue, which is consistent with the lack of effect of dietary RAC on the rate of fat deposition. β-agonist, adipose tissue.

The effects of ractopamine treatment and gender on chemical components of bacon and ham

Cured and smoked ham and bacon 20 pigs equally divided between genders (barrows and gilts) and dietary treatments (0 and 20 ppm ractopamine) were chemically analyzed for specific components (fat, Na, K, Cl and NO2). Cuts from gilts had higher contents of K and NO (P &lt; 0.05) while cute from barrows exhibited higher contents of Na and Cl (P &lt; 0.05). Cuts from ractopamine-treated pigs had higher contents of Na, Cl, K and NO2 (P &lt; 0.05) However, the observed differences in chemical composition between barrows and gilts and between control and ractopamine treatments may be attributable to differences in fat content. Composite results illustrate the chemical composition of ham and bacon from barrows and gilts and confirm the effect of dietary ractopamine in reducing carcass lipids. Key words: Pork, ham, bacon, chemical composition

Responses to homeostatic signals in ractopamine-treated pigs

The beta-agonist ractopamine (RAC) promotes protein deposition with little effect on fat deposition in the pig. To assess whether the lack of effect on fat deposition was due to changes in response to homeostatic signals, eight crossbred gilts (73 kg body weight (BW)) with venous catheters were used to examine plasma metabolite and hormone concentrations before and after intravenous injections of insulin and the beta 2-agonist fenoterol during dietary RAC (0 or 20 mg/kg) treatment. Pigs received intravenous challenges of insulin (1 microgram/kg BW) on days 3, 9 and 23 and fenoterol (2 micrograms/kg BW) on days 4, 10 and 24 of treatment. RAC was then withdrawn from the diet and insulin and fenoterol challenges were repeated 6 and 7 d later respectively. Blood samples for the determination of metabolite and hormone concentrations were taken at -30, -20, -10, -1, 2.5, 5, 10, 20, 30, 45, 60 and 120 min relative to the challenges. Dietary RAC decreased basal plasma insulin concentrations but had no effect on plasma glucose or non-esterified fatty acids (NEFA). Hypoglycaemic responses to insulin were not affected by RAC while the anti-lipolytic effects of insulin tended to be augmented. Dietary RAC decreased the lipolytic response to fenoterol, this being evident after 4 d treatment. Hypoglycaemic response to fenoterol was not changed whereas the hyperinsulinaemic response to fenoterol was attenuated by dietary RAC. Previous treatment with RAC did not influence basal hormone and metabolite concentrations or responses to homeostatic signals during the withdrawal period. While these results suggest little change in glucose metabolism, the de-sensitization of adipose tissue beta-adrenergic receptors is consistent with the observations that dietary RAC has little effect on the rate of fat deposition in the growing pig.

Temporal response of plasma metabolites to ractopamine treatment in the growing pig

Eight crossbred gilts (73 kg liveweight) were surgically prepared with indwelling venous catheters to examine the temporal pattern of circulating metabolites and hormones during dietary ractopamine (RAC, 0 or 20 mg kg-1) treatment for 24 days. Pigs were bled every 2 h for 24 h on days 1, 2, 8, 22 of treatment and again 5 days after withdrawal of RAC. Dietary RAC increased liveweight daily gain and decreased feed consumption : liveweight gain by 37 and 25%, respectively. There were no differences in growth performance between the two groups of pigs during the week after withdrawal of RAC. Dietary RAC had no acute or chronic effects upon plasma concentrations of non-esterified fatty acids (NEFA) or glucose. Likewise, plasma NEFA and glucose were not different during the withdrawal period. Plasma urea nitrogen began to decrease after 24 h of dietary RAC treatment, and remained lower than for the controls for the duration of RAC treatment. Withdrawal of RAC caused a marked increase (21%) in plasma urea nitrogen. Dietary RAC decreased plasma insulin and negated the normal increase with age in plasma IGF-I. These metabolic data are consistent with increased protein deposition with little change in fat deposition during dietary RAC treatment.

Effects of feed treatment and gender on the flavour and texture profiles of cured and uncured pork cuts. II. Ractopamine treatment and dietary protein source

A total of 128 barrows and 128 gilts were equally and randomly allocated to two separate barley-based diets containing two distinct protein sources (soybean meal and canola meal). Subsequently, the pigs within each gender/ diet treatment subgroup were equally and randomly assigned to two ractopamine treatment groups (0 or 20 ppm). The feeding trial lasted an average of 42 days. The pigs went on trial at an average weight of 67·9 kg and were slaughtered at an average weight of 101·9 kg. Ten pigs selected at random from each gender/diet/ractopamine subgroup were utilized for detailed palatability evaluation. These comprehensive palatability evaluations were conducted on both cured and uncured pork cuts. Results revealed no differences of practical importance in flavour, texture, or cooking properties attributable to dietary protein source or to administration of ractopamine, despite the fact a few statistically significant differences were observed. Thus, ractopamine can be administered with different dietary protein sources to improve production efficiency and improve carcass composition, without influencing palatability and cooking properties, or consumer acceptance. Gender effects have been reported elsewhere (Jeremiah et al., 1994b).

The effects of feed treatment and gender on the flavour and texture profiles of cured and uncured pork cuts. III. Effects of gender

A total of 384 pigs (192 barrows and 192 gilts) was utilized to evaluate the effects of gender on the flavour and texture profiles of cured and uncured pork cuts. Observed differences in all cuts indicated the incidence, intensity, and/or order of appearance of flavour character notes were more appropriate, in samples from barrows than in samples from gilts; differences observed in all cuts also indicated textural properties were more appropriate, in samples from barrows than in samples from gilts. However, the magnitude of such differences in all cuts, was insufficient to influence flavour and texture amplitude ratings. Consequently, even though cuts from barrows are marginally superior to cuts from gilts in both flavour and texture, this superiority is unlikely to be of practical importance. The effects of ractopamine treatment and protein level (Jeremiah et al., 1994a) and ractopamine treatment and protein source (Jeremiah et al., 1994b) have been previously covered.

Effects of feed treatment and gender on the flavour and texture profiles of cured and uncured pork cuts. I. Ractopamine treatment and dietary protein level

Equal numbers of barrows (64) and gilts (64) were randomly allocated to two separate diets containing 17·6 and 19·6% crude protein. Subsequently within each gender/diet treatment group, pigs were equally and randomly assigned to two ractopamine treatment groups (i.e. 0 or 20 ppm ractopamine), resulting in 16 pigs per gender/diet/ractopamine subgroup. The feeding trial lasted an average of 41 days, and the pigs went on trial at an average weight of 64·5 kg and were slaughtered at an average weight of 98·2 kg. Five barrows and five gilts were subsampled at random from each gender/diet/ractopamine subgroup for palatability evaluations. Comprehensive palatability evaluations were conducted on both cured and uncured pork cuts. Results revealed no meaningful differences in flavour, texture, or cooking properties attributable to dietary protein level (17·6 vs 19·6% crude protein) or to ractopamine. Thus, within the context of conditions employed in the present study, ractopamine can be administered with different dietary crude protein levels to improve production efficiency and carcass composition, without influencing palatability and cooking properties or consumer acceptance. Gender effects have been reported elsewhere (Jeremiah et al., 1994).

Skeletal muscle growth and expression of skeletal muscle αs-actin mRNA and insulin-like growth factor I mRNA in pigs during feeding and withdrawal of ractopamine

Sixty crossbred barrows were used to study the effect of ractopamine (a phenethanolamine/beta-adrenergic agonist) treatment and its withdrawal on muscle growth and on the relative abundance of skeletal muscle alpha-actin (sk-alpha-actin) mRNA and of liver and longissimus muscle IGF-I mRNA at 4 wk. Ractopamine was fed (20 ppm) for periods of 2, 4, and 6 wk (six pigs per group). Additional pigs (four per group) were fed ractopamine (20 ppm) for 6 wk and then slaughtered 1, 3, and 7 d after withdrawal of ractopamine. Ractopamine increased (P < .05) longisimus muscle weight and protein content, although protein concentrations were not different. The increased muscle weight and protein content attained by feeding ractopamine for 6 wk was retained when ractopamine was withdrawn. The RNA and DNA concentrations did not change, whereas total DNA and RNA content per muscle was 18 and 26.7% greater, respectively, in ractopamine-treated pigs at 4 wk, but there were no differences at 2 or 6 wk or among the withdrawal groups. The relative abundance of sk-alpha-actin mRNA in the longissimus muscle was 41 and 62% greater (P < .05) in treated animals at 2 and 4 wk but was similar to that in controls at 6 wk and during the withdrawal period. The relative abundance of IGF-I mRNA in liver and longissimus muscle was not altered with ractopamine treatment for 4 wk. These results indicate that the ractopamine-enhanced muscle growth may result from increased myofibrillar gene expression at the pretranslational level, which is maximal with short-term treatment of ractopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Genotype and treatment biases in estimation of carcass lean of swine.

Carcasses of 181 barrows, representing five genotypes, 1) H x HD, 2) SYN, 3) HD x L[YD], 4) L x YD, and 5) Y x L (H = Hampshire, D = Duroc, SYN = synthetic terminal sire line, L = Landrace, and Y = Yorkshire), and two levels of ractopamine (RAC) treatment (0 and 20 ppm) were completely dissected and the data were used to examine genotype and treatment (RAC) biases in estimation of fat-standardized lean weight and to evaluate accuracies and precisions realized by use of equations based on variables derived from different technologies. Independent variables used to establish regression equations represented technologies of direct carcass measurements, optical probe data, TOBEC (total body electrical conductivity) readings, and dissected (DHMLN) and fat-standardized (FSHMLN) ham lean. Genotype bias existed when any equation from a single technology was used and was minimized by combining FSHMLN with one TOBEC reading, carcass length, and the probe measurement of 10th rib fat depth. Large RAC biases appeared when equations from direct carcass measurements or optical probe data were used and were minimized by an equation using either DHMLN or FSHMLN. A practical equation with relatively high R2 value and small genotype and RAC biases were developed by combining TOBEC readings with direct carcass measurements of 10th rib fat depth and warm carcass weight.