Influence of the age of the first calving on some indicators of productive qualities of brown swiss cows in the conditions of the industrial complex

Presented the results of the research of the influence of different ages of the first insemination and the first calving of Brown Swiss cows on the realization of productive potential and reproductive qualities in a large industrial complex. Researches during 2019–2021 were conducted on the first-heifers of cows (n=242 cows) on the dairy industrial complex "Ekaterinoslavsky" of Dnipropetrovsk region. According to the age of the first calving, were formed five groups of first-heifers: group I (n=27) first calved at the age of 22.7 months, and fertilized – at the age of 13.4 months; group II (n=80) were first fertilized and calved at the age of 16.3 and 25.5 months, respectively; group III (n=56) – 18.9 and 28.1 months, respectively; IV group (n=38) – respectively 22,1 and 31.3 months; V group n=41 – respectively 26.5 and 35.8 months. The age of the first calving of experimental cows of all five groups differed at the level of P<0.001. It was found that the level of average daily milk yield of Swiss first-heifers of different ages at the first calving has a significant intergroup difference. Cows of II and III groups are characterized by high and almost identical indicators, in which they are 30.0 and 30.3 kg, respectively. Slightly lower average daily milk yield is observed in Swiss animals of IV group, in which it does not exceed 29.0 kg, which was inferior to the first-heifers of II group by 3.45 %, and animals of III group – by 4.29 %. Relatively the lowest average daily milk yield is characterized by the first-heifers of I group, in which it does not exceed 28.8 kg, which practically was equal to the milk yield of IV group of Swiss animals and was less than cows of II and III group by 4.17 and 5.21 %, respectively. The highest level of average daily milk yield in first-heifers of I group, in which it did not fall below 32.2 kg. This figure exceeds the animals of II and III groups by 6.83 % (P<0.05) and 5.90 % (P<0.05), respectively. In comparison with the first-heifers of IV and V groups, animals of I group have higher milk yields per day by 9.94 % (P<0.01) and 10.56 % (P<0.01), respectively. It was found that in the researches, the mass fraction of milk fat of all groups of first-heifers was close and ranged from normal to 3.93 % to 4.07 %, and protein – an average of 3.31–3.53 %. The ratio of fat and protein averaged 1.16-1.20, which is normal. It was found that the highest rate of milk yield during 305 days of lactation have first-heifers of the first group, who calved at the age of 22.7 months and have a milk yield of 9810.4 kg. At the same time, the milk productivity cows of II group, which calved at the age of 25.5 months, averaged 9140.0 kg, which is 7.33 % less than I group cows (P<0.05). In the first-heifers of III group, which calved for the first time at the age of 28.1 months, the level of milk productivity averages 9251.8 kg of milk, which is inferior to the first-heifers of I group by 6.04 % (P<0.05). Swiss first-heifers of IV group, in which the first calving was at the age of 31.3 months, have a milk yield of 8832.2 kg of milk, which is 11.08 % less than the rate cows of I group (P<0.01). Relatively the lowest level of milk productivity during 305 days of lactation is characterized by first-heifers of V group, in which the age of the first calving averaged 35.8 months. Only 8789.8 kg of milk was obtained from these animals, which is 12.32 % less than the first-heifers of I group (P<0.01). The total production of milk fat and protein in the first-heifers of I group is the highest and averages 711.3 kg, which is 7.0 % more than animals of II group (P<0.05). It is investigated that Swiss first-heifers of different ages of the first calving are characterized by satisfactory indicators of reproductive function, which are associated with a high level of milk productivity and do not depend on the age of the first calving. Compared to the biological norm in these cows, the service period is 1.76–2.24 times longer, the lactation period is 1.28–1.42 times longer, and the period between calving is 1,19–1,30 times. The adaptation index in all groups of first-heifers has a small negative value, which ranged from ˗5.89 to ˗8.23 units, which indicates satisfactory adaptive qualities in the conditions of intensive technology.