Long-term economic use of high-yielding animals is an indisputable prerequisite and the most important factor in the effective life-long use of dairy cattle, ensuring high profitability and competitiveness of the industry in the context of market relations formation. Therefore, more and more actuality is becoming a matter of finding ways to increase productive longevity of cows. The purpose of the work was to study the dependence of productive longevity of dairy cows on their yield level for the first and the best lactations.

The studies were undertaken on cows of Holstein, Ukrainian Black-and-White and Ukrainian Red-and-White dairy breeds. Retrospective analysis of the duration and effectiveness of life-long use of cows was carried out using the method of Yu. P. Polupan (2010). The sample includes the information of the primary zoo technical account of 15 farms of different regions of Ukraine (Ivano-Frankivsk, Lviv, Volyn, Rivne, Ternopil, Vinnitsa, Kyiv, Cherkasy, Chernihiv and Kirovograd).

It is well-known that the duration and effectiveness of productive use of cows is influenced by their yield level for the first lactation. At the same time, the intensive increasing the milk yield of heifers does not only reveal the potential of full-age cows, but it can also lead to a reduction in the terms of their productive use. We found that the heifers of the Holstein breed, whose yields for the first lactation did not exceed 5500 kg, were used in the herd for the longest – 2.79 lactations. With the increase of cows yields for the first lactation of over 5500 kg, their life expectancy, productive use and the number of lactations in life declined, and life-long yields and the life-long amount of milk fat, on the contrary, were highly (P <0.001) increased (with the exception of the heifers with yield of 7501- 8500 kg) and the maximum value was obtained with the yields of heifers of 8501-9500 kg. The yields for the first lactation of more than 9500 kg led to a decrease in their life-long productivity, but this decline was unreliable.

The heifers of the Ukrainian Black-and-White breed with yield of up to 5500 kg observed the highest rates of life expectancy, productive use and the number of lactations per life. Increasing their productivity over 5500 kg of milk caused, in almost all cases, a significant decrease (P<0,05-0,001) in the mentioned indicators. The highest life-long yields and life-long amount of milk fat was characterized by cows that whose yields for the first lactation were of over 10,500 kg. According to these indicators, they were highly reliable (P<0.001), overwhelmed the same age heifers with yields of up to 9500 kg.

Cows of Ukrainian Red-and-White breed with yields for the first lactation up to 5500 kg had the highest rates of life expectancy, productive use and the number of lactations in life, and the animals with yields for the first lactation of over
8500 kg, had highest lifelong diet and the life-long amount of milk fat.

Many scientists have proven that the length and efficiency of productive use of cows has a significant impact on their yields for the best lactation. It was established that the best indicators of productive longevity were characterized by animals of Holstein breed, whose yields for the best lactation were more than 10,500 kg. In all cases, they had significantly higher life-long yield rates (P<0.01-0.001), productive use (P<0.01-0.001), lactation per life (P<0.05; P<0.001), life-long yields (P<0.001) and life-long amount of milk fat (P <0.001) compared with cows whose yields for the best lactation did not exceed 10500 kg. It was noted that with yield increase for the best lactation, the age of manifestation of best lactation increased and animals with more than 10500 kg of yield reached the maximum value of 2.64 lactations.

Cows of Ukrainian Black-and-White with yields for the best lactation of 5501-6500 kg had the highest life-long yields and cows whose yields reached 9501-10500 kg had the highest duration of productive use and the number of lactations per life. Cows, whose yields for the best lactation reached more than 10,500 kg had the highest life-long yields and life-long amount of milk fat. Cows with yields of 9501-10500 kg had the highest age of the best lactation manifestation (2.24 lactations).

The optimum yield for the best lactation for cows of the Ukrainian Red-and-White breed reached more than 9500 kg, since they found the highest life expectancy, productive use, the number of lactations per life and life-long productivity for such yield. The age of the best lactation manifestation of the group was maximal and amounted to 2.55 lactations.

The power of yield influence for the best lactation on the indicators of productive longevity was somewhat higher
(23.3-25.7%) compared with the effect on these indices for the first lactation (21.8-25.1%). Yields for the first and the best lactation more significantly influenced the life-long yields (23.9 and 25.7%), productive use (23.8 and 25.5%), and the number of lactations per life (24.0 and 25.1%), than on life-long yield (22.2 and 23.5%) and life-long milk fat (22.3 and 23.6%). The correlation coefficients between yields for first and for the best lactations and indicators of productive longevity were insignificant but probable.

Key words: cows, breed, yield for the first lactation, yield for the best lactation, life expectancy, productive use duration, lactations per life, life-long yield.