First edition: I. Overview of Direct-Fed Microbials and Prebiotics and Their Interactions with the Host -- 1. The Commensal Microbiota -- 2. Prebiotics of Plant and Microbial Origin -- 3. Microbial Species Characteristics and Selection -- 4. Genomics of Probiotic-Host Interactions -- 5. The Effects of Pre- and Probiotics on the Host Immune Response -- II. Current and Future Status of Practical Applications and Challenges -- 6. Current Status of Practical Applications: Pets -- 7. Current Perspectives on Probiotics in Poultry Preharvest Food Safety -- 8. Current Status of Practical Applications: Probiotics in Dairy Cattle -- 9. Current Future Status of Practical Applications: Beef Cattle -- 10. Future Challenges of Administration of Direct-Fed Microbial Supplementation to Swine -- 11. Characteristics and Modification of the Intestinal Tract Microbiota of Channel Catfish Ictalurus punctatus -- 12. The Use of Direct-Fed Microbials as a Pre-Harvest Food Safety Intervention inCattle. Second edition with proposed changes in attachment.