Abstract
The purpose of research is to study the effect of live weight of heifers at the age of 6 months on their subsequent milk production. Objectives: to study the growth rate of heifers with different live weights at 6 months; to assess the level of milk productivity (milk yield, mass fraction of fat and protein, amount of milk fat and protein) in first-calf heifers with different live weights at 6 months. The study included more than 25 thousand first-time Holstein heifers of the same genotypes (lines), bred in four climatic zones co-vering the territory of the Russian Federation. These zones include subtropical, temperate continental, extreme continental and arctic climates. The regions of the Far North with the most severe and cold climate, unsuitable for breeding Holstein dairy cattle, were not taken into account. Data from the Selex information system were used for the analysis. Statistical processing of the obtained data was carried out on the basis of generally accepted methods of variation statistics (using MS Excel). The reliability of the difference bet¬ween the compared values was determined using the significance criterion according to the Student's table. It was found that the live weight of calves at 6 months has a certain influence on the subsequent milk productivity of first-calf heifers. However, the optimal live weight varies depending on the climatic zone. Thus, in a subtropical climate, the optimal live weight is more than 175 kg; in a temperate continental climate – more than 185; in a sharp continental climate – less than 166; in a harsh arctic climate – over 200 kg. These results make it possible to optimize the breeding process and ensure maximum milk production in different climatic conditions.
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