It has been found that the selection of Ukrainian Black-and-White dairy breed firstborns on the basis of milk yield leads to increasing in milk productivity with some changes in reproductive performance and reducing their productive use duration. The selection of firstborns on the basis of milk productivity results in increasing in average milk yield by 108 kg (1,9 %), milk fat – 3,5 kg (1,8 %) per every 5 % of selected cows. In particular, at 10 % selection of firstborn milk yield increases by 290 kg, 30 % – 735 kg, and 50 % – 1077 kg; the level of milk fat for the same intensity of firstborns selection increases by 9,23 and 35 kg, respectively.

During the selection of firstborns with increasing milk production, the reducing of fat level is observed (maximum by 0,04 % for the level of selection of 25 % and above), because of the negative correlation between these parameters.

The selection of firstborns on the basis of milk yield promotes genetic progress in milk productivity. Growth of annual genetic progress in milk yield in the herd LLC AF “Hlushky” is an average by 5,4 kg, the level of milk fat – 0,24 kg per every 5 % of selected firstborns. In case of 5 % firstborn selection, genetic progress in milk yield is 7,8 kg and milk fat – 0,35 kg, whereas at 50 % – it reaches 53,9 kg and 2,45 kg, respectively.

It is known that there is a negative correlation between milk productivity and reproductive performance of cows, so it is advisable to watch over the changes in reproductive performance of cows at different intensity of selection on the basis of milk yield. In the herd LLC AF “Hlushky” the average age of first cows calving is 975 days or 32 months and there are no significant differences depending on the level of firstborns milk productivity (the difference is 9 days and less).

However, some elongation of service period duration with increasing in firstborns selection intensity (an average 1,6 days per every 5 % selected cows) is observed. In this case the intensity of selection is 40−50 %, the difference is 12−16 days (P<0,05). The average length of service period of firstborns being researched is quite long − 157 days, it is nearly twice longer than the optimal one. This leads to the prolongation of the period between calving, the average length of which is 436 days.

The herd being researched shows that index fertility of J. Dohy is quite low − an average of 40,6 (for animals with an average fertility this index is 41−47). With the increasing in milk yield the index fertility index varies slightly with a range from 40,1 to 40,8.

So, selection of firstborns on the basis of milk yield leads to some extensions of the service period of cows and a slight decrease of the fertility index. It indicates the possibility of firstborn’s selection on the basis of milk yield without significant deterioration in their reproductive performance.

Selecting cows on the basis of milk yield and increasing in the milk productivity in the herd leads to reducing of productive use duration of cows by 0,1−0,5 lactation depending on the selection intensity of firstborns. However, the reduction of productive use duration of cows compensates by higher milk yield.

Effectiveness of cow lifetime duration the average milk yield per day of life characterizes more fully: in the research herd the average milk yield per day is 6,0 kg.

Despite the reduction of the cow productive use duration, the milk yield per day of life in the herd LLC AF “Hlushky” increases due to the intensity of firstborn’s selection. By selection of 5 % firstborns milk yield per day of life increases by 0,2 kg, 10−15 % − 0,3 kg, 20−30 % − 0,4 kg (P<0,05), 35 % − 0,6 kg (P<0,01), 40–50 % − 0,7 kg (P<0,001).

Selection of firstborn’s on the basis of milk yield causes a reduction of the length of their productive use duration and, consequently, decreasing the amount of calves that requires increasing young animal remount. However, due to the increase in milk productivity, the highest lifetime yield of cows and the milk yield per day of life are provided.

Selection of firstborns on the basis of the first lactation results on the one hand helps to remove cows with low productivity out the herd and leads to genetic progress on milk productivity parameters, on the other hand − requires more firstborns depending on the selection intensity. It is necessary to increase the remount of young animals though it is a significant problem for the most herds’ reproductive performance with high productivity in the light of the current situation.

Key words: Ukrainian Black-and-White dairy breed, selection, milk productivity, reproductive performance, productive use duration, lifetime productivity.