The influence of the Beta2-adrenergic agonist, clenbuterol, on lipid metabolism and carcass composition of sheep

Abstract

/j? *-adrenergic agonists have been described as “repartitioning agents” and “potential anti-obesity drugs” because of the decreased fat deposition they have induced in laboratory rodents and some domestic animals. The influences of clenbuterol, a @,-adrenergic agonist, on lipid metabolism of isolated ovine adipocytes and the carcass meat composition of suckling/grazing lambs and pen-fed weaner lambs are reported here. Clenbuterol decreased rates of lipogenesis and increased rates of lipolysis in isolated adipocytes. This suggests that clenbuterol may have induced an increased rate of the triacylglycerol-fatty acid substrate (futile) cycle in these cells. Growth rate of clenbuterol treated lambs was not different to that of controls in either growth experiment. Suckling/grazing lambs were slaughtered at a mean carcass weight of 16.0 kg which yielded 12.5 kg of boned out meat, containing 24.6% fat in control animals v 17.2% in clenbuterol treated animals or 3.2 v 2.1 kg of fat respectively. The pen-fed weaners were slaughtered at a carcass weight of 23 kg which yielded 19.3 kg of meat containing 38.3% fat in the controls v 27.5% in clenbuterol treated animals or 7.5 v 5.3 kg of fat respectively. In both experiments the ~30% reduction in fat was replaced with an equivalent amount of lean tissue. Responses to clenbuterol were similar in ewe, wether and ram lambs and clenbuterol caused no apparent local or general ill effects in any of the lambs. Clearly the metabolic consequences of treating lambs with clenbuterol are such that carcass fat deposition is decreased and protein deposition is enhanced. These responses are discussed in terms of the synthetic and catabolic biochemical mechanisms which underly both fat and protein accretion in the meat of lambs.