Effect of beta-adrenergic agonists in animal production and their mode of action

Abstract

Beta-adrenergic agonists cause a shift in carcass composition of poultry, pigs, cattle and sheep. Fat content is dramatically reduced in favour of a higher percentage of muscle. Carcass yield is usually enhanced and is accompanied by muscle hypertrophy. There is a tendency for an improved growth rate and feed conversion in poultry and ruminants. In pigs, only feed conversion was positively affected. Beta-agonists alter metabolism of several important pathways. They possess lipolytic and anti-lipogenic properties and improve nitrogen retention. Glycolysis, lactate production and oxygen consumption are increased, while plasma insulin levels are decreased and adipocytes become less sensitive to insulin. Energy expenditure is increased by beta-agonists, partly due to an extra heat production. In general, meat colour is not affected by beta-agonists. However, the increased metabolism resulted in a higher ultimate muscle pH. Meat tenderness is mostly unaltered, but the carcass may be more susceptible to cold shortening due to a decreased fat cover. Proximate analysis of the whole ground carcass or individual muscles indicated less fat and more protein and moisture.