Studies embraced 2956 black and white lowland cows /including 459 animals intended to reproduce bulls/ that began production between 1963 and 1980 and were utilized in six breeding byres at the Racot Horse Farm. Analyses have shown that the age at the first calving of the investigated cows was within the limits considered as optimum. The mothers of bulls, considering their greater breeding and utility value and the possibility of giving birth to bulls, had a somewhat longer calving period, they were used for a longer time, therefore a higher percentage had seven or more lactations. To prolong the utilization time of cows it is necessary to limit perturbances in the progeniture of cows in relation to the analyzed herds.