Influence of age and live weight at the first insemination on the productive qualities of holstainized cattle

The aim of the research was to analyze the effect of age and live weight of heifers at the first insemination on the milk productivity of first-calf heifers and to determine the optimal time for the first insemination of Holsteinized Black-and-White heifers. The results of the analysis showed that the highest milk yield was in first-calf heifers fruitfully inseminated at 14 months of age. Their milk yield was at the level of 8678 kg of milk with a fat content of 3.67% and a protein content of 3.19 %. The smallest milk yield is observed in first-calf heifers inseminated at the age of 16 months and older. The fat content in milk varies from 3.62 to 3.71 %, while the protein content varies from 3.18 to 3.28 %. The heifers inseminated when they reach a live weight of 332 to 375 kg and 386 to 395 kg have the highest milk yield. The first insemination with a live weight of heifers over 396 kg is not justified, as it did not lead to an increase in their milk yield in the first lactation. Thus, it is most effective to introduce replacement young animals into the herd at the age of 14 months when the live weight reaches 332 to 375 kg. This will reduce the time and cost of raising heifers, start receiving products faster, and increase milk production.