Effective management of dairy farming requires the creation not only of highly productive herds, but also to increase the fertility of cows and their long-term productive use. Although cattle have a long biologically possible longevity, but in practice this potential is not sufficiently used.
 Most scientists and practitioners previously considered the rational age of the first insemination of normally developed heifers to be 17–20 and even 23 months. But in recent years, most scientists have advocated insemination of heifers at 14–17 months.
 We were tasked to study the reproductive capacity and milk productivity of Holstein, Ukrainian Black-and-White (UBaWDB) and Ukrainian Red-and-White (URaWDB) dairy cows for the first two lactations, depending on age and live weight during insemination of heifers. It is planned to continue the study during the long-term economic use of cows.
 Research and production experiments were performed on cows of Holstein, UBaWDB and URaWDB breeds of the first two lactations of CJSC "Agro-Region" and SE "Chaika" taking into account the results of our previous research on breeding, age of fertilization and live weight of heifers.
 Heifers were inseminated at the age of 12–22 months at a live weight of mainly 360–380 kg.
 According to personal research and zooveterinary records, physiologically normal calvings occurred in 72% of cows and in 19% of cases the assistance was provided by 1–2 people, and in 9% of heifers and cows the births were difficult and required qualified veterinary care.
 According to the results of completed lactations, 188 first-born cows were found: the average duration of the service period (SP) was 175 days (from 114 to 212 days) and lactation (LP) 389 days (from 327 to 419 days). Hope milk for lactation was 9814 kg and for 305 days lactation – 8160 kg, daily hopes – 25.3 kg. In terms of duration of joint venture and productivity, the advantage was for younger cows.
 Experiments on 137 cows of the second lactation UBaWDB breed SE "Chaika" show that the average service period lasted 156 days and the lactation period – 355 days. During lactation, 9461 kg of milk is milked, and for 305 days – 8452 kg. The daily milk yield was 26.7 kg with an average fat content of 3.80%.
 When inseminating developed heifers aged 12–14 months (43 goals) SP for the second lactation lasted an average of 155 days (at the first lactation – 182 days). Lactation lasted 351 days, during which 10045 kg of milk was milked. When inseminating heifers at the age of 15–18 months (74 goals) SP lasted 154 days (during the first lactation – 166 days). Lactation lasted 349 days and milked 9282 kg of milk. When inseminating heifers at the age of 19–22 months (20 goals) SP lasted 162 days (with the first lactation – 176 days), and lactation – 366 days and milked 9116 kg of milk.
 The first lactation was completed by 181 cows with an average gestational age of 280 days, recovery period (RV) – 72 days, service period – 123 days, lactation period – 344 days, milk productivity per lactation – 7974 kg and daily milk yield – 23.3 kg of milk. The second lactation was completed by 171 cows with the following average indicators: duration of pregnancy – 280 days, RP – 74 days, SP – 127 days, LP – 339 days, hopes for lactation – 8125 kg and daily hopes – 24.5 kg.
 When inseminating heifers of all breeds at the age of 12–14 months the average duration of the joint venture was 102 days, at 15–18 months – 121 days and at 19–20 months – 136 days, and hopes for lactation – respectively 7170 kg, 7813 kg and 8672 kg. In the 134 Holstein cows controlled, the average duration of SP was 143 days, LP – 357 days and milk yield – 8938 kg. In cows of UBaWDB breed (98 heads) – respectively 100 days, 315 days and 7502 kg, and in cows of URaWDB breed (120 heads) – respectively 116 days, 327 days and 7215 kg.
 Conclusions.
 1. The influence of the age of heifers of Holstein, Ukrainian Black-and Red-and-White dairy breeds during fertile insemination on the indicators of reproductive capacity and milk productivity for the first two lactations has been studied.
 2. The optimal age for insemination of heifers should be considered 14–18 months with their normal individual development and live weight of 360–380 kg.
 3. The duration of the service period in cows with a normal course of labor and postpartum period is 100–120days, milk productivity of Holstein cows – 8–10 thousand kg, UBaWDB – 8–9 thousand kg, URaWDB – 7–8 thousand kg.
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Open Access
May 27, 2021
M I Bashchenko + 4
