The study was conducted at the breeding farm of the UKRAGROTECH Corporation, located in the Cherkasy region. The farm breeds Ukrainian Black-and-White dairy cattle. The assessment of economically useful traits was carried out from the first to the fourth lactation and depending on the linear affiliation. The influence of the age of first insemination on the subsequent milk productivity of cows was also studied. The analysis of milk yield depending on lactation on the farm for 305 days was within the range of 8568–10069.9 kg. The lowest milk yield was in cows in their fourth lactation, while the highest was in their second lactation. A similar trend was observed in milk yield for the entire lactation period. In cows in their fourth lactation, milk yield was 10.290 kg, which is lower than in other groups by 1.170.2 (I), 1.576.6 (II) and 1.214.7 (III) kg. The dynamics of fat content in milk during four lactations was at the level of 3.68–3.7%. The total amount of milk fat ranged from 439.1 kg (II) to 378.7 kg (IV). According to the results of the analysis of milk productivity depending on the linear affiliation, it was established that the highest milk yield per lactation was in animals of the Starbac 352790 line – 13279.2 kg. This group also had an extended service period – 152.2 days. However, it should be noted that in cows of the Eleveishn 1491007 line, this indicator was 2 days higher, but the milk yield per lactation was 1543.5 kg lower. Analysing the effect of the age of the first insemination on milk productivity indicators, it was found that the optimal indicator on the farm is 16.0 months. Animals in this group had the highest milk yield for 305 days of lactation during three lactations, ranging from 8119.05 kg to 9130.9 kg. Reproductive performance indicators depending on milk yield were the most optimal in animals with a milk yield of 8000–10000 kg. In the 12.000 kg group, there was a higher frequency of reproductive problems, manifested in an increase in the service period to 194.2 days, the intercalving period to 479.4 days, and a decrease in the reproduction rate to 0.76.
Хоменко et al. (Thu,) studied this question.