This book is based on papers presented at a symposium held in 2005 in South Africa. It brings together the most recent academic writings on modelling concepts, problems and applications of models and looks at the development, usefulness and limitations of models in pigs and poultry. Contents includes; description of growth and feed intake, modelling social systems and disease effects, nutrient flow models, energy transactions and energy feed systems, optimisation of broiler nutrition and modelling egg production in layering hens.