breed(redirected from breed nucleus)
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in animal husbandry, a group of agricultural animals of one species (cattle, horses, sheep, swine) requiring the same maintenance conditions and having similar physical and economically useful hereditary characteristics. A breed usually includes a large number of animals (as many as 5,000 breeding females according to D. A. Kislovskii) to make it possible to select for and against traits within the breed, thus improving the breed further. In terms of heredity, a breed consists of unidentical individuals. However, the genetically different types within the breed—zonal types (varieties), production types (for example, the heavy and light Orlov trotters), male lines, and female families—have been arranged in a system. As a result, the breed has a composite structure allowing for genetic selection in breeding purebred animals.
Agricultural breeds were created as the result of long production activity by man. A distinction is made among primitive, stud, and transitional breeds. The primitive breeds developed under conditions of extensive subsistence farming through “unconscious” artificial selection and the strong influence of natural selection. Such breeds are well adapted to local natural conditions and show little variability. The animals are hardy and have low but universal productivity. Indigenous types are the basic elements constituting these breeds.
Stud breeds were developed under conditions of intensive market production and a high level of zootechnical sophistication. Because they depend less on natural conditions in their origin, these breeds are less stable but have greater heritability and increased variability. They are the source of many types of highly productive crossbreeds that can be bred under different natural conditions. For example, Dutch and Simmental breeds of cattle, Large White swine, and Thoroughbred riding horses are found in many countries. Most present-day breeds are stud breeds, which are bred principally to obtain lines of the outstanding males and families of outstanding females. The primary method of improving breeds is purebred breeding, the highest stage of which is breeding by lines.
Most breeds of agricultural animals were developed between the late 18th century and the mid-19th century. In the USSR, approximately 60 new breeds have been developed, and all low-productivity local breeds have been greatly improved.
REFERENCESKislovskii, D. A. Razvedenie sel’skokhoziaistvennykh zhivotnykh. Moscow, 1951.
Borisenko, E. Ia. Razvedenie sel’skokhoziaistvennykh zhivotnykh, 4th ed. Moscow, 1967.
E. IA. BORISENKO