Abstract: In order to estimate variance components 8843 test day milk and fat yields records from first lactation Najdi cattle were used. Data obtained between years of 1989-2005 by animal breeding station of Najdi cattle located in Shooshtar city. Random regression models were studied in respect of different orders of fitting for fixed and random regression. Also, different methods of residual variance in the statistical model assume that included assumption of constant residual variance and different assumption about variable residual variance during lactation. According to the obtained results, the assumption of heterogeneous residual variance during lactation improved characteristics of statistical model. A suitable model with (3, 3) orders of fit for additive genetic and permanent environmental covariance functions to analyze TD fat and milk yield records were recognized. Minimum of heritability for fat and milk yield was estimated at the beginning of lactation (0.1, 0.15), respectively. The amount of this parameter increased to mid lactation and almost in the 5th month of lactation reached to maximum level (0.34 for milk yield and 0.44 for fat yield), then decreased to the end of lactation.
Key words: Random regression, milk and fat yields, Najdi cattle, residual variance, Iran
M. Nazari, M.T. Beigi Nassiri, J. Fayazi and S. Tabatabaei, 2010. Estimation of Breeding Value of Najdi Cattle Breed Using Random Regression Model. Journal of Animal and Veterinary Advances, 9: 726-729.