Effects Of Ractopamine Research Articles

Ractopamina e fitase em dietas para suínos na fase de terminação

O objetivo neste estudo foi avaliar os efeitos da ractopamina e da enzima fitase sobre o desempenho e as características de carcaça de suínos na fase de terminação. Foram utilizados 354 suínos machos castrados do tipo comercial, de mesma origem e com peso inicial de 94,1 ± 5,7 kg, distribuídos em delineamento experimental de blocos ao acaso, com seis tratamentos e cinco repetições. A unidade experimental continha 11 ou 12 animais. Como tratamentos, avaliaram-se as seguintes dietas: controle, formulada com base na tabela de necessidades nutricionais; dieta A, controle com ajuste nutricional para uso de ractopamina; dieta A com fitase; dieta A com ractopamina; dieta A com ractopamina e fitase; e dieta A com ractopamina e fitase com parte das exigências de cálcio e fósforo disponível atendida pela enzima. O experimento durou 21 dias e ao final os animais foram abatidos para avaliação de carcaças. Os resultados foram comparados por contrastes ortogonais. O consumo de ração não foi influenciado pelas dietas. A dieta com níveis proteico e aminoacídico ajustados e sem ractopamina não melhorou o desempenho dos animais em comparação à dieta controle. A ractopamina teve efeito no ganho de peso e na conversão alimentar ao final do período de 21 dias, além do peso pré-abate, peso de carcaça quente, rendimento de carcaça, carne magra total e índice de bonificação. A inclusão de fitase em dietas contendo ractopamina de forma a fornecer cálcio e fósforo disponível acima das exigências de suínos em terminação não alterou o ganho de peso, a conversão alimentar e as características de carcaça. A ractopamina melhora o desempenho e as características de carcaça. A utilização de fitase em dietas contendo ractopamina em substituição parcial a fontes inorgânicas de minerais possibilita manter o desempenho e as características de carcaça dos animais.

Effects of Ractopamine in Combination with Various Hormone Implant Regimens on Growth and Carcass Attributes in Calf-Fed Holstein Steers

The β-adrenergic agonist ractopamine (RAC) was approved for use as a feed supplement for beef cattle to increase lean muscle deposition and improve feed efficiency. The effects of several anabolic hormone implants were examined with or without RAC to determine feedlot and carcass performance of calf-fed Holstein steers. Sixteen hundred cattle were evaluated in 2 phases; cattle were divided equally into 8 treatments: 1) a nonimplanted non-RAC-fed control; 2) implanted with 20 mg estradiol benzoate plus 200 mg progesterone (EP); 3) implanted with 24 mg estradiol plus 120 mg trenbolone acetate (HT); 4) implanted with 20 mg estradiol plus 80 mg trenbolone acetate (MT); 5) nonimplanted and administered 200 mg/d RAC in the feed (R); 6) implanted with EP and administered 200 mg/d RAC (EP+R); 7) implanted with HT and administered 200 mg/d RAC (HT+R); 8) implanted with MT and administered 200 mg/d RAC (MT+R). Cattle administered RAC in both studies had increased (P < 0.05) hot carcass weight (HCW) and LM area (LMA) over cattle not fed RAC. All RAC plus implant treatments in both phases had greater (P < 0.05) HCW and LMA than the control. In addition, HCW in nearly all treatments in both phases was greater than in the R treatment group (P < 0.05). Over both phases, LMA was increased with the implant plus RAC treatments over control treatments. Ultimately, the addition of RAC in feedlot diets of Holstein steers during the last 36 d on feed increased feed efficiency and carcass lean deposition in a manner that was additive to implant effects.

Effect or ractopamine on growth and body composition of pigs during compensatory growth

The purpose of this study was to measure the growth and body composition of pigs during normal or compensatory growth from 60 to 100 kg, without (cont) or with ractopamine (rac) supplementation (20 mg/kg of diet). Thirty-four pigs were scanned by dual X-ray absorptiometry (DXA) for body composition analysis at a starting weight of 61.4 ± 0.3 kg and at a final weight of 100.4 ± 0.5 kg. Half the pigs were fed ad libitum throughout (8 cont and 9 rac). The other half were fed at maintenance for 8 weeks and then scanned again by DXA. Following the maintenance feeding, the pigs were fed ad libitum (9 cont and 8 rac) to the final weight. Compensatory growth resulted in a 30% increase in the rate of weight gain (1.23 v. 0.94 kg/day, P < 0.05), including a 44% increase in the rate of lean tissue deposition (0.90 v. 0.62 kg/day, P < 0.05), but no change in the rate of fat deposition (0.31 v. 0.30 kg/day, P > 0.05). Feeding rac resulted in a 13% increase in the rate of weight gain (1.15 v. 1.02 kg/day, P < 0.05), consisting of a 29% increase in the rate of lean tissue deposition (0.86 v. 0.67 kg/day, P < 0.05) and an 18% reduction in the rate of fat deposition (0.27 v. 0.33 kg/day, P < 0.05). The effects of ractopamine on the rates of fat and lean tissue deposition were similar for pigs continuously fed ad libitum and those experiencing compensatory growth. Both compensatory growth and the addition of ractopamine to the diet resulted in an improvement in efficiency of protein deposition; however, ractopamine also resulted in a reduction in the efficiency of energy deposition. For both growth rate and lean tissue deposition, there was an additive effect for ractopamine and compensatory growth. Thus, feeding ractopamine will enhance the growth and body composition during compensatory growth in swine.

Efeitos da ractopamina e de dois níveis de lisina digestível na dieta sobre o desempenho e características de carcaça de leitoas em terminação

Avaliaram-se os efeitos da ractopamina e de dois níveis de lisina digestível na dieta sobre o desempenho e características de carcaça de leitoas com peso corporal a partir de 85kg, durante 21 e 28 dias antes do abate, os quais foram distribuídos em delineamento experimental de blocos ao acaso com cinco repetições de dois animais por unidade experimental. Os tratamentos consistiram de arranjo fatorial 2x2, com dois níveis de lisina digestível (LD), 0,67 e 0,87%, e dois níveis de ractopamina (0 e 5ppm). Observou-se efeito significativo do nível de LD sobre o ganho de peso e peso corporal e interação significativa (P&lt;0,05) entre o nível de LD e a ractopamina sobre a conversão alimentar e sobre a taxa de deposição de carne magra corporal. Não houve efeito significativo (P&gt;0,05) do nível de LD sobre a espessura de toucinho, profundidade de lombo e rendimento em carne magra da carcaça de acordo com avaliação da carcaça, feita in vivo. Não houve efeito (P&gt;0,05) da ractopamina sobre o consumo de ração, o ganho de peso diário e o peso corporal aos 21 e 28 dias de experimento. A ractopamina reduziu a espessura de toucinho no ponto P2 aos 21 dias e aumentou o rendimento de carne magra e a profundidade de lombo na avaliação da carcaça no frigorífico.

Effects of ractopamine and protein source on growth performance and carcass characteristics of feedlot heifers1

An experiment was conducted to determine the relationship between feeding ractopamine and different amounts of MP on growth and carcass characteristics of feedlot heifers. Seventy-two crossbred heifers (475 kg of initial BW) were fed individually a diet based on steam-flaked corn for ad libitum intake for 29 d. Heifers were implanted with 140 mg of trenbolone acetate and 14 mg of estradiol-17beta 60 d before the experiment. Treatments were arranged as a 2 x 3 factorial and included 0 or 200 mg of ractopamine-HCl (23 ppm)/ d, and urea, solvent soybean meal, or expeller soybean meal (ESBM) as the predominant protein supplement. The amounts of MP supplied by the urea, solvent soybean meal, and ESBM diets were 688, 761, and 808 g/ d, respectively, calculated according to level 1 of the NRC model. Body weights were obtained 1 d before ractopamine feeding and at slaughter. Blood samples were obtained 1 d before starting the experiment and 13 d later. Ractopamine improved ADG, efficiency of gain, carcass-adjusted ADG, and carcass-adjusted efficiency of gain (P < 0.01). For ADG, heifers demonstrated a ractopamine x protein source interaction (P < 0.05); heifers not fed ractopamine had greater ADG when fed ESBM than when fed urea, whereas for heifers fed ractopamine there were no differences (P > or = 0.10) among protein supplements. This interaction was not observed for carcass-adjusted ADG (P = 0.60). Final live weights (P = 0.02) and carcass weights (P = 0.01) were greater with ractopamine feeding. Carcass marbling scores and yield grades were not affected by ractopamine or protein source (P > or = 0.39). Plasma total alpha-amino N and glucose concentrations decreased more from pretreatment concentrations when heifers were fed ractopamine (P < 0.05). Feeding ractopamine to heifers for 28 d before slaughter improved ADG and efficiency of gain without any large effects on carcass characteristics. The MP supply does not need to be increased from that provided by finishing diets based on steam-flaked corn with urea as the primary N supplement to allow the maximal response to ractopamine by finishing heifers.

Effects of Ractopamine HCl on Escherichia coli O157:H7 and Salmonella In Vitro and on Intestinal Populations and Fecal Shedding in Experimentally Infected Sheep and Pigs

The effects of the beta-agonist ractopamine, approved for use in finishing swine and cattle to improve carcass quality and performance, were examined on two important foodborne pathogens, Escherichia coli O157:H7 and Salmonella. Ractopamine, administered to sheep before and after oral inoculation with E. coli O157:H7, increased (P < 0.01) fecal shedding and tended to increase (P = 0.08) cecal populations of the challenge strain. Pigs receiving ractopamine in the diet and then experimentally infected with Salmonella Typhimurium, had decreased (P < 0.05) fecal shedding and fewer (P = 0.05) liver samples positive for the challenge strain of Salmonella. Pure cultures of E. coli O157:H7 (used in the present sheep study), E. coli O157:H19 (isolated from pigs with postweaning diarrhea), Salmonella Typhimurium (used in the present pig study), and Salmonella Choleraesuis were incubated with varying concentrations of ractopamine to determine if ractopamine has a direct effect on bacterial growth. No differences in growth rate were observed for either strain of E. coli or for Salmonella Typhimurium when incubated with increasing concentrations of ractopamine. The growth rate for Salmonella Choleraesuis was increased with the addition of 2.0 mug ractopamine/ml compared with the other concentrations examined. Collectively, these results indicate that ractopamine may influence gut populations and fecal shedding of E. coli O157:H7 and Salmonella. Because ractopamine is currently approved to be fed to finishing cattle and swine immediately before slaughter, any potential for decreasing foodborne pathogens has exciting food safety implications.

Effects of ractopamine on performance and composition of pigs phenotypically sorted into fat and lean groups1

Crossbred barrows (n = 144; 80 kg) from four farrowing groups were phenotypically selected into fat (FAT) and lean (LEAN) pens using ultrasound. The difference in 10th-rib fat depth between the LEAN and FAT groups was > or =0.5 cm. Within a farrowing group, pigs were assigned to pens (five pigs per pen and eight pens per phenotype) to equalize pen weight and fat depth. Pigs were fed a corn-soybean meal diet containing 19% CP, 1.0% added animal/vegetable fat, and 1.1% lysine (as-fed basis). Half the pens received 10 ppm (as-fed basis) of ractopamine (RAC) during the 28-d finishing phase. At 7-d intervals, live weight and feed disappearance were recorded to calculate ADG, ADFI, and G:F, and 10th-rib fat depth and LM area were ultrasonically measured to calculate fat-free lean and fat and muscle accretion rates. During the first 7 d on feed, LEAN pigs fed RAC gained less (P < 0.05) than FAT pigs fed RAC or LEAN and FAT pigs fed the control diet (RAC x phenotype; P = 0.02); however, RAC did not (P > 0.25) affect ADG after the second, third, and fourth weeks, or over the entire 28-d feeding period. Although wk-2 and -3 ADG were higher (P < or = 0.03) in LEAN than in FAT pigs, phenotype did not (P = 0.08) affect overall ADG. Dietary RAC decreased (P < or = 0.05) ADFI over the 28-d feeding trial, as well as in wk 2, 3, and 4, but intake was not (P > 0.20) affected by phenotype. Neither RAC nor phenotype affected (P > 0.10) G:F after 7 d on trial; however, RAC improved (P < or = 0.04) wk-3, wk-4, and overall G:F. Lean pigs were more efficient (P < or = 0.05) in wk 2 and 3 and over the duration of the trial than FAT pigs. Ultrasound LM accretion (ULA) was not (P > or = 0.10) affected by RAC; however, LEAN pigs had greater (P < or = 0.02) ULA in wk 2 and 4 than FAT pigs. Although fat depth was lower (P < 0.01) in RAC-fed pigs than pigs fed the control diet, ultrasound fat accretion rate indicated that RAC-pigs deposited less (P = 0.04) fat only during wk 4. In addition, calculated fat-free lean (using ultrasound body fat, ULA, and BW) was increased (P < 0.05) in RAC pigs after 3 and 4 wk of supplementation. In conclusion, RAC enhanced the performance of finishing swine through decreased ADFI and increased G:F, whereas carcass lean was enhanced through decreases in carcass fat and increases in carcass muscling.

Development of a model to describe the compositional growth and dietary lysine requirements of pigs fed ractopamine.

The objective of this research was to use recent ractopamine research data to develop an updated mathematical model to describe the daily compositional growth of pigs fed ractopamine. Mean increases of 18.2, 23.1, and 25.0% for daily protein accretion were assumed for 5, 10, and 20 ppm of ractopamine for an overall gain of 40 kg of BW gain during the feeding period. The relative effect of ractopamine described the rapid increase and subsequent decrease in the effect of ractopamine as a function of BW gain or days on test and ractopamine concentration (RC, ppm). The reduction in ME intake produced by ractopamine was described as 0.036 x (RC/20)(0.7) multiplied by the ME intake for the first 20 kg of BW gain, and then increasing to 0.078 x (RC/20)(0.7) at 40 kg of BW gain feeding period. The ratio of fat-free muscle gain to protein accretion increased by 14 to 16% with the feeding of ractopamine, depending on the dietary lysine/essential AA levels. The ratio of carcass fat gain to empty body lipid gain was increased when lysine and essential AA requirements were met. Daily protein accretion and fat-free lean growth were described as functions of dietary lysine/essential AA intakes. The percentage of lysine in protein accretion increased with the feeding of ractopamine from 6.80 to 7.15%, depending on ractopamine concentration. Equations predicting carcass measurements, such as fat and longissimus muscle depths from carcass weight and composition, were modified to incorporate prediction biases produced by ractopamine. For the four concentrations of ractopamine (0, 5, 10, and 20 ppm, respectively) during a 78 to 110 kg of BW feeding period, the model predicted performance levels for ADG (1.03, 1.15, 1.16, and 1.16 kg/d), gain:feed (kg of ADG/kg of ADFI; 0.360, 0.401, 0.412, and 0.425), dressing percentage (75.1, 76.0, 76.3, and 76.4), percentage fat-free lean (48.7, 51.0, 51.5, and 52.2), longissimus muscle area (38.8,41.8,42.5, and 43.5 cm2), 10th-rib fat depth (22.1, 19.8, 19.3, and 18.7 mm), and fat-free lean gain (321, 446, 467, and 495 g/d), comparable to recent research data. The model allows the effect of ractopamine to be added to farm specific pig growth curves. It can be used to evaluate ways to optimize the use of ractopamine, including duration of ractopamine feeding, concentration of ractopamine, and dietary lysine concentration.

Effects of ractopamine (paylean) dose and feeding duration on pig performance in a commercial finishing facility (2002)

A total of 1,035 gilts were used in a 28- day trial conducted in a commercial research facility to determine the influence of ractopamine (PayleanTM) dose (4.5 or 9.0 g/ton) and feeding duration (7, 14, 21, or 28 days prior to slaughter) on pig performance and carcass composition. Ractopamine supplementation at 4.5 g/ton for 14 to 28 days, and 9 g/ton for 7 to 28 days, improved (P<0.05) ADG by 26 to 35% (0.35 - 0.46 lb/d) and F/G by 16 to 20% (0.64 to 0.79) during the 28-days prior to slaughter. Due to these improvements in growth, carcass weights increased 8 to 10 pounds over controls. Fat depth and lean percentage improved (linear, P<0.01) with increased feeding duration. Ractopamine dose did not affect carcass lean parameters. However, carcass yield improved (P< 005) when ractopamine was fed at 9.0 g/ton. Feed cost per pound of gain increased (P<0.01) with increasing feeding duration for Paylean and was greater (P<0.05) for pigs fed the 9.0 g/ton dose for 28 days as compared to the control. However, feeding ractopamine at 4.5 g/ton for 14 to 28 days and 9 g/ton for 7 to 28 days improved income over feed costs by $3.53 to $ 4.76 per head compared to pigs fed the control diet. Return over feed costs improved due to the increased carcass weights and improved feed efficiency with the greatest values achieved with a 14 to 21 day feeding duration. These data indicate feeding ractopamine at either 4.5 or 9.0 g/ton for 14 to 21 days prior to slaughter is a cost-effective strategy to optimize return while minimizing increases in feed cost per pound of gain.; Swine Day, Manhattan, KS, November 14, 2002

Response of C2C12 mouse and turkey skeletal muscle cells to the beta-adrenergic agonist ractopamine.

The effects of ractopamine (RAC) and ractopamine stereoisomers (RR, RS, SR, and SS) on cyclic AMP (cAMP) production, total protein, and DNA concentrations in mouse skeletal muscle cells (C2C12) were evaluated. The RAC (10 microM) caused an approximately 30% increase in cell number, protein, and DNA concentrations in myoblasts after 48 h; no differences were found in myotubes. The RAC-stimulated increase of these variables in myoblasts was blocked by the presence of equimolar concentrations of propranolol. At a later passage, myoblasts failed to exhibit an increase in cell number, protein, or DNA upon exposure to RAC. Both myoblasts and myotubes increased cAMP production in response to 10 microM RAC. The RAC isomers ranked RR >> SR > RS approximately SS in ability to stimulate cAMP production, with essentially no response to SS. The SR produced about 50% of the RR response. Coincubation of propranolol (10 microM) and RAC (10 microM) prevented RAC-stimulated cAMP production in myotubes but not in myoblasts (approximately 35% of cAMP produced by RAC alone). Turkey satellite cells (derived from biceps femoris of 12-wk-old toms) produced essentially no increased cAMP when exposed to 10 microM RAC stereoisomers. Stability of RAC was evaluated under laboratory storage and culture conditions. The RAC was stable for more than 4 mo when stored in deuterated DMSO (>98% purity) at room temperature or in aqueous solutions at -80 degrees C, as determined from sequential nuclear magnetic resonance studies. Radiolabeled RAC was incubated for 72 h in the presence of serum-containing medium, with or without C2C12 cells. Ninety-eight percent of the parent compound found in the medium at time zero was present in the medium as parent at the end of 72 h. The cellular cAMP response to RAC through beta-adrenergic receptors seems to be stereospecific. If the state of myoblasts and myotubes in vitro reflects the in vivo state, then the ractopamine effect in vivo on cellular processes (including cell division and protein and DNA accumulation) may be independent of beta-adrenergic receptors in muscle.

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

Effect of ractopamine on growth performance, carcass composition, and cutting yields of pigs slaughtered at 107 and 125 kilograms.

At approximately 68 kg live weight, crossbred barrows and gilts (n = 144) were allocated to be fed to one of two weight end points (107 kg and 125 kg). Pigs from each weight group were treated with Ractopamine (RAC) (0, 10, or 20 ppm; n = 24/ treatment for the last 40 kg of gain. Feed consumption and weight gain were measured. Pigs were slaughtered and carcass measurements made at 24 h postmortem. Carcasses were fabricated into wholesale, trimmed wholesale, and boneless wholesale cuts for cutting yields. Hams were separated into muscle, fat, and bone. The RAC improved growth characteristics and carcass characteristics. Pigs fed RAC had increased (P < .01) average daily gain and improved (P < .01) feed:gain ratio over controls in each weight group. Carcasses from pigs treated with RAC had larger (P < .01) longissimus muscle area and reduced (P < .01) fat at the 10th rib. Cuts from 125-kg pigs were generally heavier than those from 107-kg pigs. The RAC increased (P < .05) the boneless cut weights of both weight groups. Percentage of dissected lean from the hams of RAC-treated pigs was (P < .05) higher than that of controls. Few consistent differences were observed between the 10 and 20 ppm of RAC treatments. Results from this study indicate that RAC had positive effects on the growth characteristics, carcass characteristics, and carcass cutting yields of pigs representative of the broad spectrum of market weights.

Effects of ractopamine on the growth and carcass quality of entire male and female pigs fed ad libitum or at a restricted level

Abstract The efficacy of ractopamine (Rac) at 0, 5, 12.5, or 20 mg/kg of the diet for entire male and female pigs of a lean genotype was assessed in two experiments. In Experiment 1 (n ‐ 56) pigs were fed a diet containing 16.5% crude protein ad libitum for 40 days from an initial weight of c. 50 kg, whereas in Experiment 2 (n = 80) the same diet was fed at a restricted level (c. 87% ad libitum) according to liveweight from 50 kg to a final weight of 87 kg. For Experiment 1 (ad libitum) Rac had no effect on growth rate of either sex and no effect on carcass composition for males, but for females the carcass lean content increased and carcass fatness decreased. For Experiment 2 with pigs fed at a restricted level, Rac increased the rate and efficiency of growth, the killing‐out percentage, and the carcass lean percentage for both sexes, but levels of fatness were not affected. Rac had no effect on Warner‐Bratzler shear force values for either experiment, but for Experiment 1, the longissimus muscles from f...

Dietary protein concentration and daily feed allowance influence response of channel catfish, Ictalurus punctatus (Rafinesque), to ractopamine

Year-1 channel catfish, Ictalurus punctatus (Rafinesque) (average initial weight, 48 g) were fed diets containing 240 g kg−1, 300 g kg−1, or 360 g kg−1 dietary protein with 0 or 20 mg kg−1 ractopamine to satiation and diets containing 240 g kg−1 and 360 g kg−1 protein with 0 or 20 mg kg−1 ractopamine at a restricted rate (60% of satiation) in aquaria at 29 ± 2°C for 8 weeks. Fish fed ractopamine at the 360 g kg−1 protein level gained significantly more weight than controls when fed to satiation but not when the ration was restricted. Fish fed ractopamine at the 240 g kg−1 protein level did not gain more weight than the controls at satiation or restricted feeding. Fish fed ractopamine in the diet containing 300 g kg−1 protein gained significantly more weight than controls when fed to satiation. Ractopamine caused no significant differences in feed conversion at the 240 g kg−1 or 360 g kg−1 protein levels with restricted or satiation feeding. Muscle fat decreased when ractopamine was fed at all dietary protein levels and at both feeding rates. Muscle protein increased with ractopamine feeding in all treatments except the high-protein, satiation treatment. Weight gain response of year-1 channel catfish to ractopamine is dependent upon nutrient concentration of the diet and ration size; however, the effect of ractopamine on muscle composition of channel catfish is less dependent on nutrient concentration or amount of diet fed.

The effect of ractopamine on beta-adrenoceptor density and affinity in porcine adipose and skeletal muscle tissue.

We have evaluated the effect of feeding ractopamine (Rac), a phenethanolamine lean enhancer being developed for commercial use in finishing pigs, on beta-adrenoceptor (beta-AR) number and ligand-receptor binding affinity in adipose and muscle tissues. Pigs weighing 78 +/- 1 kg were fed Rac (20 mg/kg of diet) for 0 (control), 1, 8, or 24 d before being killed at 105 +/- 1 kg BW. beta-adrenoceptor density (per milligram of protein) was decreased by Rac up to approximately 50% in both the middle and the outer layers of subcutaneous (SQ) adipose tissue. Orthogonal contrasts indicated significant (P < or = .05) linear effects of Rac in middle and outer SQ adipose tissue, and also a significant (P < or = .05) quadratic effect of Rac in the middle layer. Ractopamine did not affect the maximal binding (Bmax) of longissimus muscle. The relative affinity with which the beta-AR population of the tissues examined bound the radioligand ([3H]dihydroalprenolol) was not influenced by Rac. Likewise, feeding Rac had no effect on the affinity of the beta-AR for Rac. The data indicate that a Rac-induced reduction in the Bmax of adipose tissue may account for the diminished in vitro lipolytic potency of exogenous Rac after prolonged periods of Rac feeding, and that Rac-induced desensitization differs between adipose and skeletal muscle tissues.

Effect of ractopamine on carcass characteristics and joint-cartilage soundness in finishing pigs

One hundred and fifty crossbred pigs (Camborough × Canabrid, equal numbers of gilts and barrows) at an average live weight of 64.2 kg were randomly assigned to diets containing 17 or 20% crude protein (with 0.8 or 1.1% lysine, respectively) and 0 or 20 ppm ractopamine. Pigs were slaughtered at an average live weight of 102.2 kg. Supplementation of ractopamine in pig diets significantly increased average daily gain (P &lt; 0.005) and decreased feed to gain ratio (P &lt; 0.001), with no effect on daily feed intake. Ractopamine feeding increased total lean (P &lt; 0.001) and decreased total bone (P &lt; 0.05) and total fat content (P &lt; 0.001) of carcasses. The decreased fat content was largely due to the reduction of subcutaneous fat (P &lt; 0.001). Cartilage visual scores and cartilage uronic acid concentrations of weight-bearing areas of humeral and femoral condyles were not affected by feeding ractopamine. Correlations between visual scores and uronic acid concentrations of joint cartilage and performance parameters and carcass characteristics were not significant. These results demonstrated that feeding ractopamine can increase pig growth rate and carcass leanness without detrimental effect on joint cartilage. Key words: Ractopamine, growth rate, uronic acid, cartilage, osteochondrosis, pigs

The effect of feeding the beta-adrenergic agonist ractopamine on the behaviour of market-weight pigs

A total of 86 ad libitum fed Lacombe bred barrows and gilts weighing on average 90 kg were used to determine the effect of feeding ractopamine on animal behaviour. Four treatment groups consisted of a control (N = 22) and three levels of ractopamine (10 ppm (N = 15), 15 ppm (N = 24) and 20 ppm (N = 25) in the diet). The pigs received the ractopamine treatments for 5–6 wk prior to behavioural observations. There was little effect of ractopamine on behaviour. The ractopamine-fed pigs were observed to lie down in a group more frequently (P = 0.06) and to walk around their pen less frequently (P = 0.01). No abnormal, stereotyped, agonistic or aggressive behaviour was induced by the ractopamine. The data from the present study suggest that ractopamine, added to the diet of market-weight pigs at levels reported, does not cause marked changes in behaviour. Key words: Pig behaviour, beta-adrenergic agonists, ractopamine

The effect of ractopamine on myofibre distribution and morphology and their relation to meat quality in swine

One hundred and twenty-eight purebred Lacombe pigs (equal number of barrows and gilts) were assigned to one of four treatments at 64 kg and fed a commercial grower-finisher diet ad libitum to which ractopamine (RAC) was incorporated (0, 10, 15 or 20 mg kg −1). Pigs were slaughtered at 100 kg. Histological samples were collected from the semimembranosus (SM) and the psoas major (PM) muscles from the 0 and 20 mg kg −1 RAC groups. Meat quality and muscle composition data were collected for all pigs. A significant 3-way interaction for muscle weight involving treatment, muscle and gender (P = 0·01) indicated that for the SM, gilts appeared to respond to RAC at a lower level of incorporation (10 mg kg −1) than barrows. Despite these differences in response at the gross muscle level, responses were similar at the cellular level for both muscles. The proportion of red fibres did not change (P = 0·21), the proportion of intermediate fibres decreased (P = 0·01) and the proportion of white muscle fibres increased (P = 0·02) in the mg kg −1 RAC group compared to the controls. In addition, when compared to controls, average fibre diameters in the 20 mg kg −1 RAC group remained constant in the red fibres, and increased significantly in both the intermediate and white fibres (P = 0·01 and 0·02, respectively). Over both muscles Kramer Press values were significantly higher (P = 0·030 in the RAC-fed pigs than in the controls. Incorporation of RAC into the diet did not result in any changes to crude protein or total and soluble hydroxyproline levels. Crude fat tended to increase in the 15 mg kg −1 RAC treatment in the SM and decreased in the 20 mg kg −1 RAC treatment in the PM. The shift in fibre type, and the associated changes in fibre size, may contribute to the increased shear values found in RAC-fed pigs.

Effect of ractopamine on growth, carcass traits, and fasting heat production of U.S. contemporary crossbred and Chinese Meishan pure- and crossbred pigs1

Twenty-four U.S. crossbred (Duroc x White composite; D x Wc; 83.9 kg), 24 purebred Meishan (M; 59.4 kg), and 24 Meishan x White composite crossbred (M x Wc; 83.4 kg) barrows were allotted within genotype to a 16% CP corn-soybean meal diet or this basal diet + 20 ppm of ractopamine and allowed ad libitum access to feed for 52 d. No genotype x ractopamine interactions were detected (P greater than .05) in pigs for growth, lean cuts, ham and loin characteristics, leaf fat and visceral organ weights, fasting whole-animal heat production, and carcass traits except longissimus muscle area (LMA). The LMA was increased by ractopamine in D x Wc and M x Wc pigs (P less than .05) but not in M pigs. Compared with D x Wc and M x Wc pigs, M pigs had lower ADG, ADFI, and gain to feed ratio (G/F), shorter carcasses, and lower dressing percentage, LMA, predicted amount of muscle, weights of trimmed picnic, loin, and ham cuts, percentage of ham lean, and CP in ham lean, but heavier liver, kidneys, pancreas, and entire gastrointestinal tract with greater percentage of ham fat and ham bone (P less than .05). The M x Wc pigs had lower ADG, G/F, dressing percentage, LMA, amount of muscle, weights of trimmed cuts, and percentage of ham lean but heavier lungs, pancreas, stomach, and large intestine than did D x Wc pigs (P less than .05). Supplemental ractopamine increased ADG, G/F, dressing percentage, amount of muscle, trimmed loin weight, percentage of ham lean, and CP in ham lean and decreased weights of heart, lungs, kidneys, and pancreas in pigs (P less than .05). Neither genotype nor ractopamine had any effect on 4- to 24-h postprandial whole-animal heat production of pigs (P greater than .05). These results indicate that ractopamine will improve growth performance and carcass leanness in pure- and crossbred Meishan pigs.