Insulin-like growth factor-1 (IGF-1) is a 70 amino acid, single chain polypeptide hormone and an important regulator of cell growth and differentiation. Most fetal and adult tissues synthesize IGF-1 although the liver is the major source of IGF-1 found in the circulation. During fetal like circulating IGF-1 levels are low, however, after birth, concentrations gradually increase. Considerable evidence supports a primary role for IGF-1 in regulation of postnatal growth.
Most IGF-1 occurring in plasma and other body fluids is bound to one of 6 identified IGF binding proteins (IGFBP). These binding proteins prolong the half-life of IGF-1 in plasma and may either potentate or inhibit IGF-1 effects on body tissues. The concentration of individual IGFBPs in body fluids therefore has a significant impact on the biological activity of circulating IGF-1.
Plasma concentration of IGF-1 is mediated by a complex interaction among nutrient quantity and quality as well as other factors such as stress and disease. These factors are also likely to influence the circulating concentration of IGFBP. Knowledge of the changes in blood levels of IGF-1 and IGFBP under current swine management conditions may provide a basis to determine the impact of various management practices on piglet growth and welfare.