The effect of the age and live weight of Russian black pied heifers with a proportion of Holstein blood at the first insemination on subsequent milk productivity indicators

The article presents the results of research on the influence of age and live weight of Russian Black Pied heifers with a proportion of Holstein blood at the first insemination on the indicators of subsequent milk productivity. The study of the effect of live weight at the first insemination on subsequent milk productivity showed that the animals of group I with the lowest live weight (357 kg) at the first insemination had the earliest age of the first insemination - 13.5 months, which is less than the other groups by 1-4.8 months, and the earlier age of the first calving - 23.4 months. The highest indicators of dairy productivity of first-calf cows were also recorded in group I. The milk yield of the first-calf cows of this group was 9232 kg, which is higher than the milk yield of their peers of the other groups by 159-369 kg or 1.8-4.2%. During 305 days of the first lactation, 359.1 kg of milk fat and 302.8 kg of milk protein were obtained from the cows of group I, which is 2.6-9 kg (0.7-2.7%) and 4.3-10.3 kg (1.4-3.5%), respectively, higher than those of their peers from the other groups. The highest coefficient of milk production was observed in the first-heifer cows of group I with a live weight at the first insemination up to 370 kg. According to the third lactation, the level of milk productivity was higher in the cows inseminated for the first time at the age of 14.5 months with a live weight of 370-400 kg. The largest amount of milk fat - 428.6 kg and protein - 351.7 kg was obtained from the highest-yielding cows of group II. The difference in the amount of milk fat between the groups averages 3.9-14.7 kg, or 0.9-3.5%, in the amount of milk protein - 1.4-13.6 kg, or 0.4-4%.