This book explains the role of hormones in improving and monitoring the production, performance, reproduction, behaviour and health of livestock animals, focusing on cattle, pigs, sheep, horses, poultry and fish. Beginning with the principles of endocrinology and the methods to study endocrine systems, it then covers the different endocrine systems that affect different aspects of animal production and describes how these systems can be manipulated or monitored to advantage. The mechanism of action is covered, and common mechanisms and themes highlighted in order to understand potential methods for altering these systems, and stimulate ideas for the development of new methods.