Effects of Dietary Lysine Supply on Plasma Concentrations of Growth-Related Hormones in Late-Stage Finishing Pigs

The regulation of key metabolic pathways responsible for muscle protein turnover by dietary amino acids (AAs) in pigs is closely associated with the concomitant responses of some growth-related hormones. This study was undertaken to investigate the effects of dietary lysine supply at different levels on blood plasma concentrations of 3 key growth-related hormones in late-stage finishing pigs: insulin, growth hormone (GH), and insulin-like growth factor 1 (IGF-1). Nine crossbred (Large White × Landrace) finishing pigs (initial BW 94.4 ± 6.7 kg) were assigned to 3 dietary treatments according to a randomized experimental design (3 pigs/treatment). Three corn and soybean meal based diets were formulated to meet the NRC (2012) requirements for various nutrients except for lysine, whose concentrations were 0.43, 0.71, and 0.98% (as-fed basis) for Diets 1 (lysine-deficient), 2 (lysine-adequate), and 3 (lysine-excess), respectively. The feeding trial lasted 4 weeks, during which time the pigs were allowed ad libitum access to the experimental diets and fresh water. After 4 weeks, blood was collected from the jugular vein, and plasma samples were separated by centrifugation. The plasma concentrations of 3 hormones were measured by using 3 respective commercial assay kits. Data were statistically analyzed with the GLM Procedure of SAS (v9.4) with P ≤ 0.05 and ≤ 0.10 as significant difference and a tendency, respectively. Results showed that there were no differences in the plasma insulin and GH concentrations (P > 0.10) among the three dietary treatments, which suggests that the plasma insulin and GH levels of the late-stage finishing pigs were not affected by the dietary lysine concentration, at least at the range from 0.43 to 0.98%. The plasma IGF-1 concentration of the pigs fed either Diet 1 or 3, however, was lower (P < 0.05) than that of the pigs fed Diet 2, which suggests that either dietary lysine deficiency or excess can lead to a lower level of plasma IGF-1 concentration in late-stage finishing pigs. Therefore, it can be concluded that IGF-1, instead of insulin or GH, in the blood circulation may be a controlling growth factor in response to dietary provision of lysine for regulating muscle growth in late-stage finishing pigs. This study was supported by a USDA-NIFA’s Hatch/Multistate Project (under No. 1007691).