Effects of Dietary Lysine Levels on the Plasma Concentrations of Growth‐Related Hormones in Late‐Stage Finishing Pigs

This study was undertaken to investigate the effects of dietary lysine on the plasma concentrations of three growth‐related hormones in pigs. Nine late‐stage finishing barrows were assigned to three dietary treatments according to a completely randomized experimental design (3 pigs/treatment). Three corn and soybean meal‐based diets were formulated to contain three levels of lysine, which were 0.43, 0.71, and 0.98% for Diets 1 (lysine deficient), 2 (lysine adequate), and 3 (lysine excess), respectively. The feeding trial lasted 4 weeks, during which the pigs were allowed ad libitum access to the diets and water. After the 4 weeks, blood was collected and plasma samples were obtained. Then, the plasma concentrations of insulin, growth hormone (GH), and insulin‐like growth factor 1 (IGF‐1) were measured. No difference in the plasma concentration of insulin or GH among the three treatments was found (P > 0.10). However, the plasma IGF‐1 concentration was lower (P < 0.05) in the pigs fed Diet 1 or 3 than fed Diet 2, suggesting that either dietary lysine deficiency or excess can lead to a lower concentration of plasma IGF‐1. It was concluded that IGF‐1, instead of insulin or GH, in the blood may be a key controlling growth factor in response to dietary lysine supply for regulating muscle growth in late‐stage finishing pigs