Longevity of dairy cows depending on the age of first calving

Research to study the traits of duration of use and cows productive longevity of Ukrainian Black-andWhite dairy (UBWD) and Holstein breeds, depending on the age of frst calving, was carried out in the herd of PE "Burynske" Pidlisniv branch of Sumy district. The division of animals into gradations, depending on the age of frst calving, established that higher indicators of the duration and efciency of lifelong use were observed in animals of both breeds that frst calved at the age of 25.1-26 months. Early, before 24, and late, over 26 months, frst calving shortened lifetime, productive period, number of calvings, and reduced lifelong milk yield and milk fat. With an increase in the age of frst calving in UBWD and Holstein cows, a gradual reduction in lifetime and productive use reached a difference in these indicators between the best (25.1-26 months) and the frst calving group of more than 30 months, respectively 332 and 491 and 523 and 628 days (P<0.001). The influence of the age of frst calving on the lifetime productivity of cows of the UBWD breed was evidenced by a signifcant difference in favor of animals with the frst calving at 25.1-26 months, compared to the group of frst calving before 24 months, which was 3432 and 127 kg, respectively, in terms of lifetime milk yield and milk fat (P<0.001). The difference when comparing the groups of the frst calving older than 26.1 months by lifetime milk yield and milk fat was, respectively, 2082-12896 and 70-486 kg (P<0.001). The highest indicators of traits characterizing the longevity of Holstein cows, lifetime and productive use, were also obtained from the group of animals of the frst calving at the age of 25.1-26 months. According to these traits, there was a signifcant difference in their favor compared to the group of frst calving up to 24 months (282 and 173 days; P <0.05) and groups older than 26.1 months. (247-523 days; P<0.05-0.001 and 337-628 days; P<0.01-0.001). Animals of the frst calving at the age of 25.1-26 months, with a milk yield during life of 29337 kg, exceeded in this trait cows that frst calved earlier 24 months of age, with a difference in 3679 kg of milk (P <0.001) and animals with an age of frst calving older 26.1 months with a difference of 1790-12990 kg (P<0.05-0.001). By lifetime milk fat yield, the difference between these comparisons was 135 kg (P<0.001) and 56-486 kg (P<0.05-0.001), respectively. Key words: Ukrainian Black-and-White dairy, Holstein, lifespan, productive use, frst calving, lifetime productivity.