IN T RODUC T ION Beta-agonists, or β2-adrenergic agonists are, often used as drugs to treat asthma and other pulmonary diseases. They act on the β2-adrenergic receptor and cause smooth muscle relaxation, resulting in the dilation of bronchial passages and other effects. However, some beta agonists have been used illegally in meat husbandry, since they can also promote muscle growth instead of f...

Ractopamine hydrochloride is a xenobiotic that belongs to a large group of ß2-adrenergic agonist compounds. ß2-Agonists are used in human and veterinary medicine for treatment of lung diseases as bronchodilators, tocolytics and heart tonics (Courtheyn et al., 2002; Malucelli et al., 1994; Meyer & Rinke, 1991). Besides their legal use, these drugs are often misused as growth promoters, to improv...

The objective of this study was to examine the effects of growth-promoting technologies (GP) and postmortem aging on longissimus lumborum muscle fiber cross-sectional area (CSA), collagen solubility, and their relationship to meat tenderness. Two groups of black-hided crossbred feedlot heifers (group 1: = 33, initial BW 430 ± 7 kg; group 2: = 32, initial BW 466 ± 7 kg) were blocked by BW and as...

An experiment was conducted to evaluate the effects of increasing concentrations crude glycerin, with or without ractopamine, in diet finishing barrows on carcass characteristics and pork quality. The experimental design a randomized complete block, 4 x 2 factorial scheme, four glycerin (0, 100, 150, 200 g/kg) two ractopamine (0 10 mg/kg). There no interaction between use as well there isolated...

Introduction Paylean® (ractopamine hydrochloride) was approved in December 1999 by the U.S. Food and Drug Administration for use as a feed ingredient in commercial pork production, specifically in finisher swine (Paylean® Technical Manual, 2001). Paylean® is a ß-adrenergic agonist that acts by directing nutrients away from fat deposition to increase the amount of lean pork in a carcass. Paylean...

Ractopamine-HCl (RAC) is a beta-adrenergic agonist with variable effects on cattle performance and carcass variables. Cull cows fed RAC (200 mg . head(-1) . d(-1)) demonstrate an increased size of type I and II muscle fibers that does not translate into a larger ribeye area. The objective of this study was to examine the dose-dependent effects of RAC on cull cow muscle morphometrics. Eighty-eig...

Growth performance and carcass characteristics of physically castrated (PC) and immunologically castrated (IC) pigs fed ractopamine hydrochloride (RAC; 5 mg/kg) were evaluated in 64 pens of 22 pigs each. Male pigs were randomly assigned to castration method at birth. Pigs in the PC group were physically castrated at 5 d of age while IC pigs were administered Improvest at 11 and 18 wk of age. Pi...

The objective of this study was to evaluate the effects of coadministration of ractopamine-HCl (RAC) and trenbolone acetate plus estradiol (TBA) on LM fiber cross-sectional area (CSA), diameter, fiber-associated myonuclei, and satellite cell number. Culled crossbred beef cows (n = 98; 11 +/- 1.8 yr old; BCS 4.3 +/- 0.03) from a single ranch in south Florida were fed a concentrate diet for 92 d ...