Samchyk D. The results of estimation and use of servicing bulls in developing the Ukrainian black-and-white dairy breed of Polissya type.

The thesis considers the process of breed development and the role of servicing bulls in it. There have been shown the results of studying the breed and lineage structure of the servicing bulls used for the development of Ukrainian black-and-white dairy breed of Polissya type. On the leading regional pedigree farms the servicing bulls have been estimated by the productivity of the nearest female ancestors as well as by the descendants efficiency. Servicing bulls prepotency depending on their related breeds of black-and-white root, lines and genotypes has been studied. There has been considered the authenticity of estimation of servicing bulls by their descendants different number, the herds with different rate of cow milk productivity includingly. Servicing bulls of foreign selection including Holstein breed failed to be the best breed-improvers as the results of "genotype - environment" contradiction . That's why their use in Polissya region should be accompanied by the radical improvement of cattle feeding and housing. The use of holsteinized servicing bulls possessing 65-75 % of Holstein heredity proved to be the most efficient. Special affection has been paid to the formation of breeding structure of Polissya type. Key words: breed, line, servicing bulls, milk productivity, breeding value indices, female ancestors, descendants, prepotency, the category by estimation.