Milk productivity indicators (length of lactation, milk yield per 305 days, fat yield), economic usage (longevity, productive usage duration, economic usage coefficient) and lifetime productivity (number of calves per cow, lifetime milk yield, lifetime fat yield + protein yield, milk yield per one day of life and one day of lactation) of 421 Ukrainian Black and White Dairy breed cows were studied.

Reproductive performance of Ukrainian Black and White Dairy breed cows in LLC «Agro-Start» Cherkassy region for the period of 2001–2004 and 2009–2012 have undergone some changes: there were reduced age at first calving (–179 days, p<0,001), duration of dry period (–3 days) and economic usage coefficient (–0,05, p<0,05), but there were increased length of service period (+29 days, p<0,05), calving interval (+24 days) and insemination index (+0,37). This confirms the general trend of deterioration of reproduction in dairy herds.

It was established that the extension of the service period length increased the length of lactation, milk yield and fat yield for the lactation. Length of lactation in the group of cows with length of service period 211 days or more was higher 182 days (p<0,001) compared with the group of cows with length of service period 60 days and less; the difference in milk yield between these groups was 1266 kg (p<0,001), fat yield – 45 kg (p<0,001). For the length of lactation, milk yield per 305 days and fat yield significant difference was observed since the 121-st day of service period. Higher milk yield per 305 days and fat yield had cows with length of service period 181–210 days – 5663 kg and 203 kg, respectively. They dominated on these indicators cows with length of service period 60 days and less by 1624 kg (40%) and 57 kg (39 %), cows with length of service period 61–90 days – 1623 kg (40 %) and 56 kg (38 %), 91–120 days – 1564 kg (38 %) and 54 kg (36 %), respectively.

For fat content in milk significant difference between groups of cows with different length of service period were not found.

In a result of our research it was found that the longevity of Ukrainian Black and White Dairy breed cows in the herd LLC «Agro-Start» was in the range of 2433 to 2684 days, productive usage duration – 1396–1671 days or 3,51–4,04 lactations, economic usage coefficient – 0,60–0,64 depending on length of service period.

The best indicators of economic usage characterized cows with length of service period from 91 to 180 days (economic usage coefficient = 0,64), cows with lower and higher length of service period had less longevity, productive usage duration and economic usage coefficient. That is, the length of service period affects the value of cows’ economic usage indicators.

In the herd LLC «Agro-Start» from each cow during the lifetime was got 3,15–3,76 calves depending on length of service period. More calves, higher lifetime milk yield, lifetime fat yield + protein yield and milk yield per one day of life were got from cows with length of service period from 91 to 180 days: calves for the period of productive life – 3,73 heads (on average in groups of cows with length of service period 91–120, 121–150, 151–180 days), lifetime milk yield – 19,185 kg, lifetime fat yield + protein yield – 1371 kg, milk yield per one day of life – 7,16 kg. The largest advantage by lifetime milk yield and milk yield per one day of life was found in groups of cows with length of service period 91–120 days (+2835 kg; +0,5 kg, respectively) and 151–180 days (+3416 kg; +0,7, p<0,05) compared with similar indicators of cows with length of service period 60 days and less.

Milk yield per one day of lactation depending on length of service period in the research herd were within 13,8–14,9 kg. There is a tendency of reducing its value by lengthening of service period length. Significant lower milk yield per one day of lactation was observed in cows with length of service period 121–150 days (13,8 kg, p<0,01) and 211 days or more (13,9 kg, p<0,05).

Effect sizes calculations (η²_x) of service period length on indicators of milk productivity, economic usage and lifetime productivity of Ukrainian Black and White Dairy breed cows by method of analysis of variance showed, that its value was different – from 6,2 % to 49,5 % and varied depending on the indicator.

Among researched milk productivity indicators the significant impact the length of service period had on length of lactation (35,7 %, p<0,01); among economic usage indicators – on longevity (32,3 %, p<0,05), productive usage duration in lactations (27,4 %, p<0,05) and economic usage coefficient, which depends on longevity (24,3%, p<0,05); among lifetime productivity indicators – on number of calves per cow (41,4 %, p<0,01), lifetime milk yield (49,5 %, p<0,001), lifetime fat yield + protein yield (47,7 %, p<0,001).

The influence of the length of service period on indicators of milk productivity, economic usage and lifetime productivity of cows is the basis for improving the breeding efficiency in dairy herds.

Key words: Ukrainian Black and White Dairy breed, service period, milk productivity, economic usage, lifetime productivity.