The traditional scientific system of animal nutrition has existed for over 100 years, but substantial changes are yet to take place. With the lapse of time, limitations of this traditional scientific system have been more and more evident and such a system should be dramatically revised with innovations. Beginning in the late 1980s, our group started to use system-science principles and approaches in animal nutrition research. The author published a book entitled "An Introduction to Systems-Nutrition of Animals", which marked the birth of a new scientific system in animal nutrition to stimulate further development of this discipline. System-nutrition is defined as a branch of biological sciences that concerns system-level studies of the integrative picture of flux, metabolism, utilization and regulation of nutrients (e.g., proteins and amino acids) from dietary and endogenous origin in the whole animal system at organism, organs, tissues, cells and molecules levels to achieve such goals as nutritional manipulation and prediction, as well as optimum feeding decision and optimum nutritional engineering programs for animal feeding.