The article presents the results of a study on the variability of reproductive performance traits in Ukrainian Black-and-White dairy cows depending on genetic and breeding factors. The research was conducted at the State Enterprise Experimental Farm «Oleksandrivske» in Vinnytsia region using firstcalf cows and retrospective analysis of zootechnical records. The study focused on live weight at first calving, age at first calving, and duration of the fi st service period. The infl uence of sire origin, line affiliation, parental mating methods, and breeding systems on the development of reproductive traits was evaluated. It was established that the average live weight of cows at first calving was 520,6 kg, the average age at first calving was 27,4 months, and the average duration of the first service period was 168,8 days. A signifi cant effect of sires on the reproductive traits of their daugh ters was revealed. The daughters of the bull Zhames were characterized by the highest live weight and the oldest age at first calving, whereas the longest service period was observed in the daughters of Ladonis. Significant inter-line differences were identified for the studied traits. First-calf cows of the Starbuck line were distinguished by a higher live weight at first calving, whereas animals of the Haneve line had the greatest age at first calving. The longest service period was recorded in cows of the Elevation line. It was proven that intra-line and inter-line mating affect the formation of reproductive traits differently. Under intra-line breeding, animals of the Starbuck line demonstrated the highest live weight at first calving, whereas under inter-line mating the best indicators were observed in first-calf cows of the Kavaler × Starbuck cross. The advantage of purebred breeding over crossbreeding in terms of early maturity was established. An increase in the proportion of Holstein heredity to more than 93,7 % resulted in a decrease in the age at first calving; however, no significant deterioration in other reproductive performance traits was detected. The obtained results indicate the expediency of considering genetic factors in breeding and selection programs aimed at improving the reproductive efficiency of dairy cattle.

Keywords: Ukrainian Black-and-White dairy breed, first-calf cows, reproductive performance, live weight, sires, line affiliation, intra-line and inter-line mating, purebred breeding and crossbreeding, breeding and selection work.