Influence of dietary lysine level on whole-body protein turnover, plasma IGF-I, GH and insulin concentration in growing pigs

Abstract

Abstract Four growing pigs (initial liveweight 25.9 ± 0.54 kg, final liveweight 43.0 ± 1.06 kg) were used to study the effect of dietary lysine level on nutrient digestibility, whole-body protein turnover, plasma insulin-like growth factor-I (IGF-I), growth hormone (GH), insulin, glucose, and urea nitrogen (PUN). Four diets, containing 7.0 g (L1), 9.5 g (L2), 12.0 g (L3) and 14.5 g (L4) lysine per kg diet respectively, were formulated as experimental treatments. The animals and diets were allocated in a 4 × 4 Latin square design. Nitrogen (N) metabolism and whole-body protein turnover were measured by classical method and single-dose 15 N end-product method, respectively. The blood samples were taken at the end of each experimental period. Results showed that N retention (NR) and N biological value (NBV) were significantly increased from L1 to L4 ( P P > 0.05). There was no significant difference on dry matter (DM) digestibility, organic matter (OM) digestibility and N digestibility between different treatments ( P > 0.05). Whole-body protein synthesis, protein degradation and protein accretion increased markedly from L1 to L2 ( P y , g/kg W 0.75 /d) increased with dietary lysine ( x , g/kg) in a quadratic manner: y = − 0.09 x 2 + 2.12 x − 5.14 ( r 2 = 0.96, n = 4, P The results also showed that differences in plasma IGF-I, GH, glucose and PUN concentration between different treatments were not significant ( P > 0.05). Plasma insulin concentration ( y , μIU/ml) was increased with dietary lysine ( x , g/kg) in a quadratic manner: y = 0.23 x 2 − 4.10 x + 32.25 ( r 2 = 0.99, n = 4, P y , g/d) and plasma IGF-I ( x , ng/ml): y = − 3.1 × 10 − 3 x 2 + 1.31 x − 122.28 ( r 2 = 0.99, n = 4, P It was concluded that dietary lysine level had a significant influence on NR and whole-body protein turnover but not on plasma IGF-I and GH concentration. Plasma IGF-I may be an important factor controlling N metabolism of growing pigs. Further research was needed to study the mechanism.