The article says that all over the world, dairy livestock is used for dairy production. They use such breeds as a black-mottled breed, Holstein, Dutch ones. Breeding livestock differs in economically useful qualities depending on the climatic and ecological-forage conditions of the breeding zone, and the gene pool of breed resources. The widespread and long-term use of the Holsteinisation, along with a positive effect, i.e., an increase in milk yield, revealed problems associated with a decrease in the reproductive functions of the livestock. The aim of the work is to study the milk yield of the Holsteinized black-mottled breed of the Ural type depending on the duration of the service period. The article notes a significant percentage of dairy cows with a service period of more than 200 days and 121-160 days. Dairy cows with a service period of up to 120 days turned out to be 32%, taking into account the presence of dairy cows with optimal insemination period of only 19%. This indicates a decrease in reproductive functions in the Holsteinized black-mottled breed of the Ural type. The change in milk yield per three lactation depending on the duration of the service period is mainly determined by the individual characteristics of dairy cows and but not on the service period. Dairy cows with a service period of 103 days have the highest milk yield indicators. Dairy cows of other groups with other duration of the service periods had milk yield by 209 - 656 kg, or 1.96 - 6.15% less. The difference was not reliable due to the significant variation in milk yield within the groups. The duration of the service period does not affect the quality indicators of milk. The optimal duration of the service period for livestock breeding, namely the Holsteinized black- mottled breed of the Ural type is considered to be 81-120 days. An increase in the duration of the service period does not lead to an increase in milk yield, but affects the duration of productive longevity of dairy cows.