Milk yield is affected by many internal and external influences. Recently, opportunity to choose a calf sex due to usage of sexed sperm is often discussed and therefore the aim of this study was to find the effect of calf sex on milk yield dam in our condition. Database of milk yield records contains 197 333 cows between years 1995-2015. Recently, american and danish studies reported the effect of calf sex but they differed in chosen sex. In our study the model with fixed regression was used and it resulted in increasing a milk yield (about 21 kg milk per lactation) when the male calf was born, which is enonomically not significant.