The study of animal can be referred to be any one of several terms. One term we have already used is animal husbandry. Traditionally, animal husbandry referred only to the meat-producing animal and to houses, did not include poultry and dairy cattle. In recent years, however the term animal husbandry as a category of agriculture has been giving way to terms such as animal science and animal industry, which generally include al farm animal. Farm animal are often referred to as livestock. Although some people use this word to refer only to the meat-producing animal, in this book the term livestock refer to all species of farm animal.