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Relevance . Holstein dairy cattle are bred in the Sverdlovsk region. To improve the efficiency of dairy cattle breeding, it is necessary to establish reference indicators for the age of first insemination of replacement heifers of a new breed formation, which will allow obtaining higher productivity indicators. The purpose of the work is to study the effect of the period of the first insemination of repair heifers on the productive qualities of cows of Holstein black-and-white cattle. Methods . To conduct the study in a typical breeding plant for the region, 4 groups were formed from among calved heifers of 35 heads each — a control group and 3 experimental ones based on the principle of pairs of analogues. The dairy productivity of cows for the first lactation, maximum lactation, and lifetime milk yield according to control milks (once a month) were evaluated. The fat and protein content in milk was assessed in an average milk sample once a month from each cow. Results . As a result of the studies, it was established that all cows had high productivity indicators. For the first lactation in 305 days, depending on the group, it ranged from 7455.5 ± 20.96 (insemination at the age of up to 15 months) to 8707.6 ± 22.1 kg (insemination at the age of over 17 months). Cows from the group inseminated for the first time at the age of over 17 months in terms of milk yield were significantly (p ≤ 0.05–0.01) superior to cows from other groups in all assessment periods — lifelong milk yield, first lactation and maximum lactation. Cows that were inseminated for the first time over the age of 17 months produce a little more than three calves on average in the group and their average productive longevity is 2.6 lactations, which is 0.2–0 more than in other groups. 5 lactations. The research is exploratory and was carried out within the framework of scientific research of the Ural State Agrarian University (state registration No. AAAAA-A19-1191014000069).
Горелик et al. (Tue,) studied this question.