Book excerpt: Fully revised and updated, this study is a significant contribution to the understanding of animal nutrition, health, and productivity. Covering an array of modern topics—from the biology of the gastrointestinal tract and the analysis of microbial populations to understanding bio-feed ingredients and the use of enzymes, oliosaccarides, probiotics, and organic acids to replace antibiotics in animal diets—this is a must-have reference for anyone involved in the animal sciences.