The study used Legendre polynomials to describe lactation curves and monitor dairy cows’ resilience. Daily milk yield observations (DMY) were analysed from 510 purebred Holstein and 165 Czech purebred Fleckvieh cows. There were monitored via Affimilk software on a farm from 1998 to 2020. The original database included 767 577 observations from 946 dairy cows and 2 795 lactations. After the data edit, it contained 527 966 DMY and 1 839 lactations from cows with days in milk (DIM) from 1 – 305. The highest completed lactation was the eighth. Individual cows’ Persistence of Milk Production (PMP) was calculated and then computed to the average PMP by breed and lactation.