Abstract
Dairy cow breeding has become highly complex as progress is made into the understanding of which genes are responsible for which traits and how well a particular trait is passed from one generation to the next. The impact of industrial use of cows on following genetic parameters: phenotypic variability, correlation, repeatability and heritability of economically useful traits in the high producing dairy cows herd of black-motley breed with the high level of Holsteins has been studied. After setting the breeding objectives it is important to decide which traits can be used to select individuals for breeding, and these traits being known as selection criteria. With the increasing the period of use cows up to 7 or more lactations, coefficients of variation of all monitored indicators declined in connection with the removal of cows with extreme indicators of productivity and longevity during first 3-4 lactations. The correlation coefficients of milk yields during the first, highest lactation and in lifetime, regardless of the period of use is closely related to the life-long milk yield, milk yield per day of productive life and milk yield per day of life. The heritability coefficients (h²) of the indicators of longevity with increasing period of use cows up to 5 or more lactations has tended to increase: by the age of first calving from 0.01 to 0.16, by the number of highest lactation from 0.18 to 0.33, by milking days from 0.10 to 0.30, by lifetime milk yields from 0.18 to 0.32, and by days of life from 0.01 up to 0.21. The highest repeatability of indicators of milk yield, milk fat, body weight of cows regardless of the duration of their use was for the adjacent lactations (1 and 2, 2 and 3, 3 and 4, 4 and 5, 5 and 6). With increasing distance of lactations from each other the coefficient of repeatability of these traits is lowered.