The duration of productive use is a complex integral feature and is determined by both genetic and paratypical factors. This feature should ensure maximum milk productivity of animals, economic efficiency of dairy farms and generally limit the cost of raising and keeping cows. Research conducted in the experimental farms of state enterprises "Kutuzovka", Kharkov district of Kharkov region using cow’s Ukrainian black-and-white dairy breed (4038 cows). We studied the duration of productive use of cows divided into gradations according to the conditional bloodline for the Holstein breed, depending on the weight in the control age periods of cultivation (at birth, at 6, 12 and 18 months). The maximum value of the duration of productive use was recorded in the group of cows with a share of conditional blood for the Holstein breed up to 30% inclusive (the average duration of productive use is 2.77 lactations). The highest indicator of the duration of productive use of the studied animals was 4.09 lactations. Among cows with a share of conditional blood for the Holstein breed up to 30% longer produced those born with a weight of more than 40 kg (4.09 lactations), at 6 months of age weighed 100-149 kg, at 12 months – 200-249 kg, at 18 months of age – 350-399 kg. Among animals with a share of bloodline of 31-60 %, those that had a weight at the age of 6 months produced the longest: 155-190 kg (3.17 lactations), at 12 months – 250-299 kg (2.98 lactations), at 18 months – 350-399 kg (3.06 lactations). In the most numerous gradation with the share of bloodline for the Holstein breed 61-90 %, the longest productive use was characterized by animals born with a weight of 30-39 kg (2.12 lactation), at 6 months of age they weighed more than 200 kg (3.29 lactation), at 12 months-300-349 kg (3.40 lactation), at 18 months – 400-449 kg (2.82 lactation). The average duration of productive use of cows of this grade is quite low – in the range of 2.82-3.29 lactations. The highest degree of influence on the duration of productive use in this gradation of animals was recorded by the live weight factor at 6 months of age (η2 = 10.8). Сcomparative assessment of the cows gradation with a share of conditional blood for the Holstein breed of 91 % or more found that the longest productive use was characterized by cows that had a live weight at birth of 30-39 kg (1.93 lactation), in 6 months – 155-199 kg (2.73 lactation), in 12 months – 250-299 kg (2.87 lactation) and in 18 months – 350-399 kg (2.62 lactation). The degree of influence of live weight at this age on the duration of productive use of cows is insignificant, except for live weight at 6 months of age (η2 = 11.8).
