a type of breeding system used to bring about radical improvement in unproductive breeds.
Simple grading-up involves mating animals of two breeds (one to be improved and the other to do the improving). The resulting hybrids are mated for several generations with males of the improving breed until the desired type of animal is obtained. Highly productive hybrids of the fourth, fifth, and sixth generations that attain the desired traits of the improving breed are inbred, sometimes resulting in the creation of a new breed. Grading-up involving several improving breeds is the quickest and most efficient method of radically improving unproductive livestock and transforming breeds (for example, changing coarse-wooled breeds of sheep into fine-wooled and semifine-wooled breeds).
The rate at which a breed can be transformed and improved depends on the extent of hereditary differences between the animals of the breeds being crossed, the degree of hereditary stability of the breeds, the care taken in selecting and matching the hybrids, and the feeding and maintenance conditions of the young hybrids. Grading-up is used to breed almost all species of agricultural animals. In the USSR it was widely used from 1925 to 1950 to increase the breed purity and productivity of commercial and breeding herds.
G. R. LITOVCHENKO