The article presents the materials of studying the influence of age and development of replacement heifers on milk production and further lifetime productivity of cows. The economic indicators of milk and lifetime productivity, duration of the use of cows for breeding purposes depending on the age of first calving and live weight were analyzed. The studies were carried out in 2009–2019 in the pedigree breeding unit of Irkutsk region. The indicators of productivity of cows of the black-andwhite breed of the Pre-Baikal type at different ages of first calving (22–28 months) were studied. The material of the work was the information database of animals from the breeding program Selex. Organizational, technological and economic research was carried out according to generally accepted methods. The ways of increasing milk and lifetime productivity of cows, increasing the profitability of dairy production on farms were determined. On the basis of the analysis, the optimal timing of calving and introducing first-calf heifers into the main herd in order to obtain profit was established 22 months from birth with a live weight of 530-540 kg. These cows showed the highest productivity during the first lactation, however, their lifetime productivity proved to be the lowest. The highest lifetime productivity was recorded in cows whose age at the first calving was 27 months; proceeds from sales of additional produce received by the farm amounted to 131191 rubles. It was found that cows whose first calving age was 28 months had a decrease in lifetime productivity (25382 kg/head), the cost of additional produce from these animals was 102577 rubles/head.
The materials of the long-term (2008–2018) research into the reproductive function of cattle of the black-and-white breed of Baikal type in Irkutsk region are presented. The influence of the age at the first insemination and live weight on cows’ milk productivity, lifelong productivity and productive longevity was studied. The experiment was conducted on the basis of materials from the breeder-farm for breeding cattle of Baikal type on the groups of cows of different ages: up to 14–20 months and older. Cows inseminated at 16 months (7917 kg) had the best milk yield in the first lactation. The largest milk yield was obtained from inseminated cows with live weight of 401-410 kg. Milk production of these heifers was 7902 kg in the first lactation, 8792 kg – in the second and 8710 kg – in the third. It was revealed that age of cows and their live weight at the first successful insemination had a positive effect on the lifelong productivity and productive longevity of cows. Cows whose age at the first successful insemination was 15 or 16 months had a longer duration of productive use (productive life span of animals was 2561–2558 days, respectively). The highest lifelong productivity (34379–34585 kg) was obtained from the cows of this group. The economic efficiency of lifelong milk production was determined depending on the age of the first insemination. The highest lifelong milk productivity was obtained from cows, which were first inseminated at the age of 15–16 months. The largest revenue from sales of additional products was also received from the cows of this group (366,058–370,480 roubles per head). The results obtained allow to develop effective methods for increasing reproductive capacity of cattle.
The results of studies on the effect of the birth season factor on the lifetime productivity and growth rate of cows are presented. The material for the research was the information database of the "Selex" breeding record program for the highly productive herd of black-motley cattle of the "Pre-Baikal type". The research was carried out under the conditions of the Irkutsk region in 20152019. Replacement heifers, which were evaluated for growth and development, and subsequently for milk production during the 1st and 3rd lactations and lifetime production, were chosen as an object of research. Heifers born in the summer-autumn period, according to the 1st lactation, gave the highest productivity, their milk yield was 6151-6179 kg of milk with a fat content of 3.85%. By the 3rd lactation, cows born in the summer months retained high productivity (7001 kg with a milk fat content of 3.83%). From the cows born in winter, a maximum lifetime production of 30,519 kg was obtained. The cows born in spring have 856 kg less lifetime productivity. With the maximum lifelong productivity, the age in lactations was 4.5, with the minimum - 4.0. This indicates that the shorter the period of productive use, the lower the lifetime milk yield of cows. The cows that gave the highest milk production in the first lactations dropped out of the herd sooner for various reasons, thereby not having reached their full genetic potential and not having shown their possible maximum milk production.
The paper presents the results of studying the effect of sire lineage on reproductive qualities and milk yield of cows. The study was carried out inIrkutskregion on a herd of Holsteinized black-andwhite cattle of Pribaikalsky type. The analysis of the main characteristics of reproductive capacity of herd cows on a farm was performed during 2013–2018. The material of the research work was based on the informational database of animals from the program of breeding register Selex. Cows were divided according to sire lineage and milk productivity into five groups by the level of milk yield: from 5000 to6500 kg, 6501-8000, 8001-9500, 9501-11000 and more than11001 kg. Successful insemination of heifers took place at the age of 15.7-16.6 months with the live weight of more than400 kg, which corresponds to zootechnical standards. The earliest (15.7 months) insemination was in heifers of Reflection Sovereign sire line, the age of first calving was 753 days with the live weight of561 kg. The latest (498 days) successful insemination was observed in heifers of Montvik Chieftain bull line with the live weight of498 kg. Cows of Sealing Trygen Rocket (8766 kg) and Reflection Sovereign (8704 kg) sire lines had the highest milk productivity with a significant difference (p ≥ 0.90). The cows of these lines had the longest service period (164 and 179 days), as well as the length of the calving interval (445 and 458 days), respectively. The coefficient of reproductive capacity of cows of different sire lines ranged from 0.80 to 0.88, which is a low indicator.
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