This volume continues the theme established in Volume 1 of providing a con­ spectus of the current state of knowledge on topics of active nutritional re­ search. It is the aim of the editors, through this series, to assist investigators in keeping abreast of developments in fields other than their own and to provide a source of reference materials for use in graduate teaching. In addition, general reviews will be published occasionally on fields of less active current research interest which have not been reviewed recently elsewhere. The quality of the contributions to Volumes 1 and 2, and of the manuscripts scheduled for publication in future volumes, gives assurance that Advances in Nutritional Research will be an asset to those engaged in research and teaching in the broad field of the nutritional sciences. vii Contents Chapter 1. Regulation of Energy Metabolism in Ruminants ...... 1 Ransom Leland Baldwin and Nathan Elbert Smith 1. Introduction ............................................. .