Much attention has been traditionally paid to the role of amino acids in protein synthesis and their requirements in animal nutrition. Recently, there is growing interest in regulatory roles of amino acids in nutrient metabolism and immune responses. They are called functional amino acids which are necessary not only to animal growth and maintenance requirement, but also to the synthesis of bioactive molecules. Remarkably, arginine can enhance conception rates, embryogenesis, blood flow, antioxidant activity, protein synthesis, immune cell proliferation, and intestinal development, thereby improve fertility, fetal and postnatal growth, and neonatal health. Therefore, large scale availability of feed grade functional amino acids holds great promise for enhancing the efficiency of nutrient utilization in pigs.