Dietary lysine and threonine utilization by young pigs: Efficiency for carcass growth

Abstract

Two experiments were conducted to determine the efficiency of dietary lysine and threonine retention for carcass protein accretion in pigs within a body weight range of 10–20 kg. At the beginning of the experiments, an initial representative group of 6 pigs were killed for carcass compositional analysis. In the first experiment, conducted to determine the efficiency of dietary lysine retention, a basal diet was formulated to contain 6 g of lysine kg−1. Twelve pigs were fed the basal diet supplemented with L-lysine∙HCl to contain 6, 7, or 8 g of lysine kg−1. Daily weight gain and gain:feed ratio were higher (P < 0.05) for pigs fed 8 g of lysine than for pigs fed 6 g of lysine kg−1 diet. The accretion rates of dry matter, protein, ash, and lysine in the carcass were higher for pigs fed 8 g of lysine than for pigs fed 6 g of lysine kg−1 diet. A linear regression of daily carcass lysine accretion on daily lysine intake resulted in a 72% efficiency of carcass lysine accretion above maintenance. In the second experiment, three diets including a basal diet formulated to contain 4 g of threonine kg−1 and supplemented with L-threonine to contain 4, 4.65, or 5.3 g of threonine kg−1 were fed to 12 pigs. Rate and efficiency of body weight gain exhibited a dose-response improvement (P < 0.05) to an increase in dietary threonine. Carcass protein, ash, and threonine accretion rates were higher (P < 0.05) for pigs fed 5.3 g of threonine than those fed 4 g of threonine kg−1 diet. Linear regression of daily carcass threonine accretion on daily threonine intake resulted in extra-maintenance efficiency of threonine retention of 60%. The efficiencies of dietary lysine and threonine utilization for carcass growth in pigs within the liveweight range of 10–20 kg are 72 and 60%, respectively. Key words: Lysine, threonine, retention efficiency, amino acids, pigs