Quality of feed nutrition is influenced not only by the content but also by some other aspects such as, feed presentation, hygiene, anti-nutritional factors, digestibility and palatability. Feed additives provide a mechanism by which such dietary deficiencies can be addressed and also benefits not only associated with the nutrition and thus the growth rate of the animal concerned, but also its health and welfare. Feed additives could modify animal metabolism in specific and direct ways by improving production efficiency (weight gain or milk yield); improving carcass composition in growing animals; increasing milk yield in lactating animals; and decreasing animal waste per production unit. This book discusses the impacts of feed additives on animal metabolism, health and production.