Implementation of the large-scale breeding principles has enabled to improve animal husbandry in short term and to create populations with high genetic potential. Due to semen and breeding animals import from abroad gene pool of valuable dairy cattle sires which can produce offspring with genetic potential for the milk yield of 6500–7000 kg has been established in Ukraine. However, only under high level of feeding and farming the high potential of the imported breeds offspring can be practically realized.

The animals productive traits are the result of the interaction of the genotype and the environment, as it is not the trait but level of the genotype response to the environmental conditions that is inherited; identifying economically useful traits is largely conditioned by the environment the animals arefarmed in.

Milk productivity is the main indicator for assessing economically useful traits in cattle. The genetic potential of cows indicates the maximum capacity. The standard in evaluation of genetic potential for milk production is the Holstein breed and it makes 10.000 kg of milk, in Ukraine.

The aim of research was to study the efficiency of Holstein breed bull-sires in making Ukrainian black-and-white dairy cattle population.

The herd AE "Svitanok" was formed as a result of the inporting 500 black- and-white Holstein heifers of German selection. The inported animals are descendants of 230 bull-sires belonging to 6 Holstein lines, i.e. an average 1–3 sires daughters per bull-sire were obtained.

The average herd performance for the first complete lactation was 6170 kg of milk with 3.49 % fat content.

However, phenotypical variability of milk production on the analyzed lines is rather high, as evidenced by the standard deviation performance and coefficient of variation, which creates real prerequisites for successful improvement of herds due to selection and choosing the best individuals on the basis of genealogical structure of the herd.

The largest share in the herd was made up by the animals belonging to Eleveyshna 502043 line, which is mainly represented by granddaughter and great-grandchildren of Starbuck 503327 bulls – 66 %, Sekseyshna – 70 %, Tradishna 682485 – 24 %. Animals of this line had an average milk yield 6153 kg ± 68.9 for 305 days of lactation, with the largest standard deviation of 949.7 kg with variability of 15.48 % and fat content in milk of 3.46±0.036 %, which is 17 kg of milk lower than the average in the herd and 0.02 % in fat. However, there are animal in this line whose productivity is far higher than the average in the herd. The research reveals that Aerostar 503398 bull daughters wich is the son of Starbuck 503327 bull had the highest milk productivity for both single-line animals and the herd on average, by 268 kg of milk and 0.36 % of fat and 251 kg of milk and 0.33% of fat respectively. herd. Kleytus 502797 and Sprays 502744 bulls daughters had high milk yield, but it was low in fat, 3.33 and 3.16 % respectively, under the same conditions.

R. Soverinh 198.998 line is represented by the famous Blekstar 502870 bull which has 94 % of lactating cows in this line, the average performance of which was 6394.5±150.62 kg of milk with milk fat 3.47±0.997 %, which is higher the average of 225 kg of milk in the herd and 136 kg in the line.

R. Soverinh 198998 line has definite breeding lines of A.Chif 1427381 and Valiant 1650414 in the herd of AE "Svitanok". Representatives of Valiant 1650414 line had the highest milk production in the herd (milk yield 6278.3±318.32 kg, milk fat 3.52±0.521 %).

High performance level of Royal II 504 025 bull granddaughters, which belong to this line as well should also be noted the (the first lactation yield was 6606.2±318.3 kg of milk with fat content of 350±0065 %). They far outweighed their peers in the yield capacity, by 436 kg of milk an average.

Lines analysisreveals that the highest milk fat in the herd had thee representatives of line Wisconsin A.B. Leda 697189 by Ned Boy 502 694 bull (3.63 ± 0.076 %, with the standard deviation of 0.44 % and variability of 12.09 %), which is 0.14 % higher than the average in the herd. These cows milk yield was 173 kg lower than the average in the herd.

Thus, the analysis of genealogical structure of AE "Svitanok" herds with regard to milk production indices indicated that special attention should be paid to the development of the four lines of Holstein Origin: Eleveyshna 502.043, M. Chif-teyna 95679, Valianta 502383 and Wisconsin A.B. Leda 697189 in further selection and breeding work with the herd through organizing deliberate selections with using valuable breeding bull-sires of Holstein breed, as well as high-quality repair herd, i.e. through the introduction of valuable firstborn cows.

Key words: population, Holstein, black-and-white dairy breed, line, bull-series.