Variance components and genetic parameter estimates using random regression models on test day milk yields of Holstein Friesians [Siyah Alacalarda Şansa Bagli{dotless} Regresyon Modelleri Kullani{dotless}larak Denetim Günü Süt Veriminin Varyans Bileşenleri ve Genetik Parametrelerinin Tahminlenmesi]

Genetic parameters for test day milk yields of Holstein Friesian cows were estimated by random regression with Legendre polynomials. The analyzes were applied to 5918 first lactation test day milk yields of 612 Holstein Friesian cows calving from 1987 to 1993 in Dalaman, Tahirova, Sarimsakli and Türkgeldi State Farms. Estimated genetic variances for test day milk yields were larger at extremes of the lactation. Permanent environmental variances mostly decreased in middle part of the lactation. The heritability values for test day milk yields were from 0.26 to 0.57. The genetic correlations between test day milk yields (TD1-TD9) with the last test day milk yield (TD10) were changed from -0.10 to 0.96 and it was high between consecutive test day milk yields, but decreased when the intervals between the test days increased. In random regression models it can be concluded that higher order polynomials were recommended for a sufficient fit of the (co)variance structures over the lactation but a reduction of the orders can also be used for computational simplicity due to small numbers of parameters