The work aims to study the features of herd reproduction in the conditions of a modern specialized unit for growing repair young animals. The studies were carried out in the conditions of Megaferma OOO in the Kuznetsky region, which is part of the Rusmolco Company in the Penza region, on the number of animals in the modern herd reproduction center. The object of the research was the replacement heifers of the Holstein breed; the subject of the research was: live weight of heifers in different technological periods and the efficiency of insemination of heifers with sexed and ordinary sperm. The studies show the dynamics of live weight of the Holstein heifers of different origin (Holland, the USA, Russia) during directed growing; the achievement of live weight of 350 kg was established by the period of the first insemination at the age 12 months; the Dutch heifers had a higher growth rate during all growing periods. The results of studies indicate that when using sexed semen, the pregnancy rate of heifers from the first insemination was 54.5%; 82.5% of heifers were received from the studied livestock, which is 29.5% more than from the insemination with ordinary semen. When inseminating with sexed semen of heifers of different origins (Hungary, Germany, Russia), the existing differences in the experimental groups were found. The pregnancy rate from the first insemination in the studied livestock ranged from 48.7 to 59.7%, and the yield of heifers - from 77.5 to 89.4%. Such indicators are consistent with the international practice of using sexed semen and with the guarantees of the semen producer. Consequently, an increase in the number of heifers in offspring allows breeding farms to abandon the acquisi-tion of expensive breeding young stock.

The origin of an animal determines its productive and breeding traits. It is well known that in dairy cattle breeding a great importance belongs to sires, especially those belonging to the leading lines of Holstein breed. The productive indicators of heifers and fi rst-calf cows the off spring of diff erent lines of Holstein breed and daughters of diff erent sires have been presented in the article. The researches have been carried out under the environments of specialized enterprises for rearing of replacement heifers and milk production. Diff erences have been found in the daughters of diff erent sires in terms of live weight and milk productivity. Accounting for the weight growth of the daughters of sires has shown that the live weight of heifers between the lines Wes Ideal 933122 and Refl ection Sovereign 198998 was not a signifi cant diff erence. Daughters of sire # 511H11283 of the line Refl ection Sovereign 198998 in all age periods had a live weight, absolute and average daily gain, the growth rate of replacement heifers was higher than the daughters of other sires. At one year of age, their live weight was higher than that of heifers-daughters of sires # 11H11596, # 11H11565 and # 511H11422, respectively, by 4,1 % (P<0,001), 3,1 % (P<0,01) and 5,0 % (P<0,001). The daughters of sire # 511H11283 of Refl ection Sovereign line also had a higher yield of calves – 104,8 %. However, the largest number of heifers (75,7 %) has been obtained from the daughters of sire # 11H11565 of Refl ection Sovereign line. In terms of milk yield, signifi cant diff erences have been found between the lines and daughters of diff erent sires. Higher milk yield was obtained from the fi rst-calf cows of line Wes Ideal 933122 (12361±321 kg) and the daughters of the sire Mogul 11H011757 (13587±328 kg). According to the mass fraction of fat and protein in milk, the duration of the period of open days and the number of inseminations, there were no signifi cant diff erences between the studied groups of animals. Thus, the infl uence of specifi c sires on individual productive indicators of daughters has been established.

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