The corresponding chapter in the previous edition of this book concluded by describing protein and energy metabolism as a unity instead of an interaction of separate components of metabolism | 15 Interactions between Protein and Energy Metabolism . Wright1 . Maas2 and . Milligan1 1Department of Animal and Poultry Science University of Guelph Guelph Ontario N1G 2W1 Canada 2Centre for Integrative Biology University of Nottingham Sutton Bonnington Leicestershire LE12 5RD UK Introduction The corresponding chapter in the previous edition of this book concluded by describing protein and energy metabolism as a unity instead of an interaction of separate components of metabolism. This edition will examine some of the recent knowledge generated about this subject with an emphasis on those metabolites and tissues that serve important roles for biochemical reactions in which carbon and nitrogen are in effect equal partners. Animals encounter numerous challenges during their lives and respond to achieve maximum advantage for their welfare and survival in meeting those challenges. This does not imply however that the response will necessarily be measured as the most efficient possible in terms of agricultural animal performance. It is possible to make estimates of the stoichiometry of numerous reactions for many metabolic pathways involving protein and energy intermediates. The opportunity for nutritionists is to develop a better understanding of the fate of nutrients under differing circumstances and of the regulatory system that determines an end point. The energetic costs associated with disposing of an amino acid AA can differ from tissue to tissue. Current models have advanced nutritional efficiency in terms of product per unit animal but it is appropriate now to explore those pivot points and signals that may determine nutrient fate and associated energetic costs of protein and energy metabolism. It will become clear that a better comprehension of the unity of protein and energy metabolism follows from the further development of quantitative models that reflect metabolic mechanisms. Rumen Aspects The initiation of ruminant protein and energy metabolism
