Over the last decade, analyses fitting the so-called random regression model have become a standard procedure for the analyses of data from livestock recording schemes, where the traits of interest are recorded repeatedly and the test day yields are considered directly. 352.159 first lactation test day milk yield records of 54.845 Holstein Friesian cows that raised in Turkey between 1995-2006 were used as material. Means of test day milk yields by month of lactation were found to vary between 16.57 kg and 22.74 kg. Genetic parameters and breeding values were estimated using a random regression model. Records were measured on the same date in a herd were regarded as a sub-group. Estimates of heritability for test day milk yields were between 0.12 and 0.15. In addition, estimates of additive genetic and phenotypic variances ranged from 2.33 to 4.49 kg(2) and from 19.57 to 29.78 kg(2), respectively.