Livestock production is a very complex system which has many interrelated components such as climate, soil, plants and obviously, animals operating with a high degree of interaction within a certain economic and social environment. Traditionally, these components have been studied separately by scientists in animal science subdisciplines such as nutrition, breeding and physiology, and in other disciplines such as range and forage science, health science, and economics. Animal scientists have long recognized that optimization of our resources for livestock production and maximization of production efficiency requires these components to be synthesized and studied in an integrative form. This has usually been attempted in an informal, intuitive and unorganized fashion due to the lack of defined theory and methodology. However, with the emergence of systems theory as a science during the last 20 to 30 years, the use of a systems approach. to the study of livestock production has received increased attention.