Влияние возраста первого отела на молочную продуктивность и качество молока

Nowadays, in order to reduce the cost of replacement heifers raising, early insemination and, accordingly, earlier use of cows are practiced in many farms. The purpose of the research is to study the relationship between milk productivity and the age of the first insemination of Holstein heifers under the conditions of OOO Kaluzhskaya Niva (a limited liability company under the laws of Russian Federation) in the Peremyshl district. The experimental groups were formed from cows with completed fourth lactation, taking into account the age of the first fruitful insemination. As the result of the study, it was found out that the optimal insemination index is observed at heifers of the first and second groups upon reaching the age of 12-14 months with a live weight of 337.6-340.9 kg. The shortage of live weight of heifers by the age of 12 months lengthens the time of raising, and reduces the effectiveness of their insemination (group 4 – the multiplicity of insemination is 3.3). The maximum growth rate was observed at heifers of the first group and made 865-931 g/day, which is 6.1-32.1% higher than in heifers of the other groups. When analyzing the dairy productivity of cows, there is a tendency to decrease the level at the second and third lactations, and an increase in the fourth lactation in comparison with the first one. More balanced lactation activity in a number of lactations is observed in cows of the third group (II lactation decreased by 2%, III - decreased by 5%, IV – increased by 17.5%, compared with the first lactation). At the same time, the variation in milk yield in cows of the other groups ranges from -9.2% to +20.6%. The differences in the indicators of the mass fraction of fat and the mass fraction of protein in milk of cows of different groups are not significant. The tendency of decrease of the mass fraction of fat in milk in cows of all groups is noted by the 4th lactation, with increase in the mass fraction of protein. Thus, for the manifestation of high milk productivity and its preservation in a number of lactation, the optimal age for the first insemination of Holstein heifers is 15-16 months.