The insulin-like growth factor (IGF) system comprises of IGF-I and IGF-II ligands, two types of IGF receptor, six species of IGF-binding protein (IGFBP) and a `secondary IGFBP`. In this communication, roles of the IGF system components as related to growth and metabolic control systems are reviewed, with a special emphasis on circulating IGFs and IGFBPs. It has been rigorously demonstrated, by studies involving transgenic and gene targeting animal models and also ablation and replacement or direct injection/infusion, that IGF-I stimulates fetal growth and development independently of growth hormone and also plays an intermediary role in growth hormone-stimulated somatic growth in postnatal animals. IGF-II also plays a similar role in fetal growth, but its role in postnatal animals is less than clear. IGFs also have an insulin-like activity in metabolic control of the carbohydrate, protein and fat as well as in the maintenance of glucose homeostasis as an auxiliary agent of insulin. IGFBPs, in general, play a modulatory role in these actions of the IGF. The IGF activity is suppressed under conditions of restricted energy and/or protein intake, which appears to be partly mediated by insulin. Unlike growth hormone, however, nutrition plays more of a permissive role than a regulatory role in the expression of IGF system components. Unfortunately, above information has been obtained mostly from clinical trials and also from studies in the rat as an animal model, although farm animal species are superior to the rat as an animal model in many aspects. More basic and interdisciplinary studies of the IGF system in farm animals as an alternative animal model and economic species are awaited.