Economic and biological characteristics of the first-calving Holstein heifers of different origin during acclimatization on a farm in Central Russia

Making the most of the genetic potential of dairy cattle imported to the Russian Federation is an important and urgent task which requires a detailed study of animals’ acclimatization and adaptation under the conditions at regional livestock enterprises. The aim of the work was to assess body scores, productive and reproductive performance, blood biochemical parameters and composition in the Holstein black-and-white first calving cows (a herd of OOO Molochnik, Bolshesoldatsky District, Kursk Province, 2019-2020). We compared performance of 15 imported heifers of European selection from Denmark (group 1) and 15 heifers from pre-adapted mother cows born on the farm (group 2). The groups were in identical feeding and housing conditions. On average, the cows calved in 23.6 (group 1) and 24.6 months (group 2), having bodyweight of 509.2 and 516.9 kg, respectively. For 305-day lactation, total milk production was 8667 kg with 3.73 % fat for group 1 and 121 kg more with 3.80 % fat for group 2 (the differences are insignificant). Milk yield adjustment to 3.4 % milk fat increased the difference to 314 kg (P > 0.95). In group 1, the milk fat yield was 323.6 kg, or 10.3 kg less compared to group 2 (the differences are insignificant). The difference in milk proteins was also small (3.27 vs. 3.28 %). Total milk protein yield was 283.4 kg vs. 288.2 kg, the milk production coefficients (i.e., fat-corrected milk yield per unit bodyweight) was 1867 kg vs. 1900 kg. Therefore, these findings confirm 93.1 % vs. 93.0 % realization of genetic potential for milk production, 99.5 % vs. 100.7 % for milk fat, and 100.0 % vs. 99.3 % for milk protein. All cows were quite tall, their height at the withers averaged 137.5 cm vs. 135.4 cm, at the sacrum 145.3 vs. 142.4 cm. The total exterior scores, including strong body constitution, well-developed milk traits, and leg condition, in group 1 were higher (P > 0.95) compared to group 2. According to a 100-point evaluation, the cows of group 1 had a slight advantage. Of the classification traits, the score of trunk volume was 0.9 points higher, of udder - 0.9 points higher, of general appearance - 0.8 points higher compered to group 2 (the differences are insignificant). The animals of both group had body type Good+ with 83.0 points vs. 81.7 points for five classification traits compared (the difference is insignificant). At month 6 of lactation, the total blood protein level averaged 83.11 g/l vs. 83.78 g/l. Other biochemical blood parameters (albumin, globulins, glucose, cholesterol, calcium, phosphorus, magnesium, activity of transamination enzymes and alkaline phosphatase) were within the physiological limits. An increased counts of blood leukocytes occurred in the European cows. The hematocrit index in group 1 was significantly higher than in group 2 (P > 0.95), which is apparently due to intensified metabolism. Thus, in the conditions that meet the biological needs of animals, the acclimatization of European breeding cows is quite successful.