Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2006.636.640EdrissM.A. M.A. Nilforooshan J.M. Sadeghi 4200694(Co)variance components and genetic parameters were estimated using Derivative-free Restricted Maximum Likelihood (DFREML) approach for milk yield and fat yield of Iranian Holsteins of Isfahan province. Data was consisted of first lactation records on milk and fat yields of 12,047 Holsteins from 45 herds, which were calved from 1995 to the end of 2001. Records were pre-adjusted to mature equivalent yields (ME-2X-305d). Six different animal models were fitted, which were differentiated by including or excluding maternal additive genetic effects, maternal permanent environmental effects and direct-maternal genetic covariance. Animal Models included Herd-Year-Season and direct additive genetic effects as fixed and random effects, respectively. Direct heritability estimates (h2) ranged from 0.157 to 0.229 and 0.203 to 0.243 for milk yield and fat yield, respectively. The estimates were substantially higher when maternal effects were ignored from the model. Mean estimates of the maternal genetic and maternal permanent environment variances and direct-maternal genetic covariance as fractions to the phenotypic variances were 0.07, 0.02 and 0.025 for milk yield and 0.01, 0.05 and 0.016 for fat yield, respectively, while, positive direct-maternal relationships (Covam) were obtained. The results of this study showed that maternal additive genetic and maternal permanent environmental effects had not any important influence on the yield of dairy cows. However, they can improve genetic evaluations. Also, there is no need for the inclusion of direct-maternal genetic covariance in the animal models for dairy cows.]]>Albuquerque, L.G., J.F. Keown and L.D. van Vleck,199881544549Albuquerque, L.G. and K. Meyer,20011188392Dong, M.C., L.D. van Vleck and G.R. Wiggans,19887130473052Duangjinda, M., J.K. Bertrand, I. Misztal and T. Druet,20017929973001Duguma, G., S.J. Schoeman, S.W.P. Cloete and G.F. Jordan,2002326675Edriss, M.A. and H. Khosravinia,2000pp: 11-36pp: 11-36Legates, J.E.,19723512941302Meyer, K.,19981998Perez, M.A., D. Hernandez, R. Alenda, M.J. Carabano and N. Charfeddine,19992317Rorato, P.R.N., J.F. Keown and L.D. van Vleck,19998215741580Schutz, M.M., A.E. Freeman, D.C. Beitz and J.E. Mayfield,19927513311341Seykora, A.J. and B.T. McDaniel,19836614861493Simm, J.,1998pp: 433pp: 433Vleck, van L.D. and G.E. Bradford,1966494552Vleck, van L.D. and C.L. Hart,1966494144Weigel, K.A., T. Kriegl and A.L. Pohlman,199982191195Willham, R.L.,1963191827