Genetic selection strategies for efficient lean growth in pigs

Abstract

Great improvements in both growth rate and carcass composition have resulted from efficient breeding programmes employed in the pig industry in recent years. Selection strategies that emphasise high efficiency of lean growth (low feed intake/lean growth), however, result in a decline in voluntary feed intake and this may further limit improvement in growth, deteriorate meat and eating quality, predispose pigs to leg weakness, and impair reproductive performance of sows. Increasing leanness has also been shown to be associated with muscles containing a low percentage of oxidative (type I and IIA) and a high percentage of glycolytic (type IIB) fibres. The physiological increase in the level of plasma growth hormone concentrations and insulin-like growth factor-I has resulted from selection for high growth and low backfat, but the physiological increase in serum leptin is primarily a response to increased fat deposition. Genotype and feeding regime interaction may exist for growth, but are unlikely to be important influences on backfat thickness, feed intake or carcass traits. Research has shown that diets with a high nutrient density fed as a restricted ration over a fixed period seem most appropriate for identifying animals with high genetic merit for lean tissue deposition and a reduced maintenance requirement. It is concluded that performance testing for growth while candidates are exposed to restricted feeding is valuable in identifying pigs with high genetic merit for lean production and that such animals are capable of performing equally well on different feeding regimes.