This book brings together the papers presented orally or as posters at the Sixth International Workshop on Modelling Nutrient Utilization in Farm Animals, held in Wageningen, The Netherlands, 6 - 8 September 2004. The purpose of this book is to present current research in modelling nutrient digestion and utilization in cattle, sheep, pigs, poultry and fish. The book is organized into six sections that cover a range of topics and modelling approaches; these are (i) absorption and passage; (ii) growth and development; (iii) mineral metabolism; (iv) methodology; (v) environmental impact; and (vi) animal production and feed evaluation. Deterministic, stochastic, empirical and mechanistic modelling approaches are described.