Genetic and environmental factors in selection of Holstein breed
The Holstein breed is one of the most widespread breeds in the world. This is due to its productive and adaptive qualities. However, in our country, for a long time, scientists and practitioners were ambivalent about the Holstein breed. This was due to the problems that arose when crossing Holsteins with local breeds. At present, in Russia, preference is given to the Holstein breed for intensive milk production. At the same time, many of the introduced massifs are poorly studied. The purpose of this publication was to study the genetic and environmental factors that influence productive traits. The productivity of animal lines of W.B. Ideal, M. Chieftain, R. Sovereign (n = 891). It was determined that there were no significant differences in the growth rate of heifers among the lines. Coefficients of variation (C<sub>v</sub>) of live weight during all rearing periods were within the normal range. A slight increase (up to 11.7%) was noted in M. Chieftain heifers from 6 to 12 months of rearing. The genotypic variability of the live weight of heifers from birth to 18 months increased from 2.11 kg to 25.87 kg. The greatest superiority in milk yield over mothers was noted in first-calf cows of the W.B. Ideal - 1463 kg of milk. With an increase in mothers' milk yield from 5000 to 7000 kg of milk, heritability (h<sup>2</sup>) increased to 0.304 in terms of milk yield, but the coefficient of heritability of milk fat content fell. The herd used the seed of 17 breeding bulls with the superiority of daughters over the herd averages from 690 kg to 2242 kg of milk. In general, in the future, the selection according to milk fat content, milk flow rate and% of protein in milk deserves special attention. Genotypic variability will allow for effective selection based on the main characteristics of selection.