Daily milk yield observations (DMY) were analysed from 484 lactations of 300 purebred Holstein and 84 lactations of 61 Czech Fleckvieh cows monitored via Affimilk software from 1994 to 2017. The database included 167 112 DMY observations between 1 and the maximum ranging from 242 to 305 days in milk. The highest completed lactation was the eighth. Using a linear model with sixth-order Legendre polynomials, the lactation curve predicted a cow’s expected milk yield on each lactation day. The deviations of DMY from the predicted milk yield, their variance and skewness (SKEW) were determined. The variance of deviations was log-transformed (LnVar) to achieve their normal distribution. There were estimated least square means for DMY, deviations, LnVar and Skew, and the significance of fixed effects and correlations between traits by statistical programme SAS 9.4® using proc GLM and proc CORR. DMY ranged between 5.1 and 54.9 kg, with a mean of 31.3 kg of milk per cow and day. DMY were higher in the Holstein breed than in the Fleckvieh breed and increased with parity. In both breeds, the deviations were significantly influenced by year and calving season and increased with parity. While differences between breeds were found for both LnVar and Skew, LnVar was mainly influenced by parity and Skew by calving year and calving season. The total number of recorded cases of clinical mastitis was 1253. Lactation incidence for the whole lactation was 95 %, in early and middle lactation 50 % and in late lactation 34 %.