ANIMAL BREEDING

controlled propagation of domestic animals. Its aim is the improvement of qualities considered desirable by humans. Breeding procedures involve the application of several basic sciences, chiefly reproductive physiology, genetics, and statistics. This article deals with the practical application of scientific principles to the selection of superior animals and the planning of mating combinations. The fundamental biological principles underlying animal breeding are discussed in the articles heredity and reproductive system, animal. Animals are bred for utility, sport, pleasure, and research. Dogs, for example, have been bred to serve as watchdogs, police dogs, hunters, sheep dogs, and pets. Many species of small mammals, especially rats, mice, rabbits, and guinea pigs, are bred for research, chiefly in genetics, physiology, and medicine. The basic principles of breeding are the same no matter what the animal species or the purpose in breeding may be, but the practical approach to the problem may differ in several respects, depending on such considerations as the mode and rate of reproduction and the relative effects of genetic and environmental factors on the traits of greatest interest. The term population is used in this article to denote a group of interbreeding individuals; i.e., a breed, or strain within a breed, which in some respects is genetically different from other breeds, or strains, of the same species. The word purebred is used here in its sense of referring to animals registered in the herdbook maintained for a certain breed, or to animals eligible for such registration, and the mating of purebred animals is called pure breeding. It is to be understood that genetically pure breeds (homozygous for all traits) do not exist. The objectives of animal breeding vary with regard to species, local conditions, and time. Early in history horses were bred mainly for riding or loading purposes; later they were bred for traction; and nowadays, to a large extent, for sport (racing and hunting). In North America and western Europe, cattle populations are specialized for beef or milk production, or bred for a combination of both. In southern Europe and in many parts of Africa and Asia, oxen are still produced for pulling plows or carts. Some breeds of sheep are specialized for wool production, some for meat, and one breed, the Karakul sheep, is bred for fur production (Persian lamb). Pigs always are bred for meat production, but they may be specialized to produce a certain type of meat, either pork or bacon. At one time, chickens were bred for the combined production of eggs and meat, but in the Western world there is now a pronounced specialization of breeds and crosses to produce either eggs or meat. the controlled propagation of domestic animals with the purpose of improving inherent qualities considered desirable by man. Animals are bred for utility (e.g., food, fur), sport, pleasure, and research. Improvement or favourable change in animals is brought about by changing the inheritance or the environment. Hereditary characteristics are those that arise from gene differences and account for common differences in animals as, for example, the white-face characteristic of Hereford cattle. Nonhereditary differences are mainly environmental; e.g., animals poorly fed and managed will not develop to their maximum capacity. Environment, if markedly improved, can bring forth changes in animals with dramatic swiftness, but the changes continue only while the improved environment prevails. Changes in the hereditary makeup of a population are made slowly, but usually are fairly permanent. Some characteristics, however, revert to the original level when man withdraws his selectivity. Additional reading Overviews include James Blakely and David H. Bade, The Science of Animal Husbandry, 5th ed. (1989); John R. Campbell and John F. Lasley, The Science of Animals That Serve Humanity, 3rd ed. (1985); M.E. Ensminger, Animal Science, 9th ed. (1991); W.J.A. Payne, An Introduction to Animal Husbandry in the Tropics, 4th ed. (1990); and Clarence E. Bundy, Ronald V. Diggins, and Virgil W. Christensen, Livestock and Poultry Production, 5th ed. (1982). Volumes in the World Animal Science series discuss, among other topics, animal health, genetics and breeding, feeds, and the production of livestock species. The principles and practices of animal breeding are described by Enos J. Perry (ed.), The Artificial Insemination of Farm Animals, 4th rev. ed. (1968); Everett James Warwick and James Edward Legates, Breeding and Improvement of Farm Animals, 7th ed. (1979); Frederick B. Hutt and Benjamin A. Rasmusen, Animal Genetics, 2nd ed. (1982); Franz Pirchner, Population Genetics in Animal Breeding, 2nd ed. (1983; originally published in German, 2nd rev. and expanded ed., 1979); and Malcolm B. Willis, Dalton's Introduction to Practical Animal Breeding, 3rd ed. (1991). Robert E. Stewart Ivar K. Johansson The Editors of the Encyclopdia Britannica