The effect of ractopamine, a phenethanolamine beta-adrenergic agonist, on growth, nutrient utilization and carcass composition was studied in two lines of pigs that were fed high (24%) or low (12%) protein diets. Of the two lines of pigs that had been selected for seven generations for rapid lean growth when fed either the higher (HS line) or low (LS line) protein diet, the HS line tended to ex...

Ractopamine is a β-adrenergic agonist used as an energy repartitioning agent in the diets of finishing pigs. Most ractopamine studies are limited to evaluations of growth performance and meat quality, and there is little information on the effects of this additive on the behavior and welfare of pigs. Therefore, the objective of this study was to evaluate various indicators of stress caused by f...

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 ...

Ractopamine, a synthetic β(2)-adrenoceptor agonist, is widely used as a feed additive in the United States to promote a reduction in body fat and enhance muscle growth in cattle, pigs, and turkeys. It has the potential for illegal use in show and racing animals because it may affect performance via its β-adrenergic agonist properties or anabolic activities. Nine greyhounds were orally administe...

The pork industry is constantly seeking economical methods which will increase production efficiency and carcass quality. Three nutritional management “tools” at pork producer’s disposal that have been demonstrated to improve growth performance and carcass characteristics are: 1) adding rendered animal fats to diets; 2) adding the recently approved feed additive ractopamine to finishing diets; ...

The present study was conducted to determine the influence of dibutyryl-cAMP (dbcAMP), epinephrine, ractopamine and clenbuterol on insulin binding to porcine adipocytes. Dibutyryl-cAMP decreased insulin binding to swine adipocytes by 40 and 20% at 1.8 and 25.8 ng insulin/ml, respectively. Ractopamine and clenbuterol directly reduced insulin binding at the low insulin concentration and decreased...

In order to prepare a high capacity packing material for solid-phase extraction with specific recognition ability of trace ractopamine in biological samples, uniformly-sized, molecularly imprinted polymers (MIPs) were prepared by a multi-step swelling and polymerization method using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, and toluene as a poro...

The objectives of this study were to determine the effects of ractopamine HCl (RAC) stereoisomers (RR, RS, SR, and SS) on performance, carcass composition, and nitrogen retention in growing female rats. Forty-eight rats (eight rats/treatment) were treated with 0 or 320 microg/d of RAC or with 80 microg/d of the RR, RS, SR, or SS stereoisomers of ractopamine. Rats had free access to feed and wat...

Ractopamine HCl is an β-adrenergic receptor (βAR) ligand that was recently approved for use in swine to enhance carcass leanness. The RR stereoisomer of ractopamine is the most active of the four stereoisomers exhibiting the highest affinity and signaling response. The RR isomer exhibits selective activation of the porcine β2AR, which might limit the lipolytic response to ractopamine because th...

Simple and reliable methods using LC/MS have been developed for the determination of the beta-agonist ractopamine in swine and cattle tissues. Ractopamine was extracted with ethyl acetate from muscle and liver, and the ethyl acetate layer was evaporated to dryness. The residue was purified by partition with acetonitrile/n-hexane. In the case of fat, ractopamine was extracted and purified by par...