THE ROLE OF GROWTH-HORMONES, BETA-ADRENERGIC AGENTS AND INTACT MALES IN PORK PRODUCTION - A REVIEW

In this review, the physiological actions and efficacy of porcine somatotropin (PST) and beta-adrenergic agonists as repartitioning agents and the use of intact males to improve the production efficiency of pork are discussed. The strengths and weaknesses of these methods are highlighted to provide insight into the potential benefits and problems from their commercial applications. The repartitioning agents alter nutrient metabolism in pigs, producing dramatic increases in lean- and decreases in adipose-tissue growth. The PST-induced decrease in adipose-tissue growth results from the reduction in rates of lipogenesis, glucose oxidation and insulin-stimulated glucose metabolism. In general, beta-adrenergic agonists reduce the rate of lipogenesis through a reduction in the number of insulin receptors and in the binding of insulin to adipocytes. Beta-adrenergic agonists also stimulate synthesis of myofibrillar protein while depressing its degradation. The natural anabolic androgens produced in the testes account for the increased lean and decreased adipose tissue of intact males compared with castrates. The effects of androgens are mediated by their interaction with specific receptors in the target tissues. The main limitation to the use of intact male pigs is the occasional presence of objectionable boar taint in the meat. The causes of and methods for measuring boar taint are discussed in this review. The implementation of effective measures for measuring and controlling taint in pork will allow the pork industry to take advantage of the biological effects of the naturally produced androgens in intact males.