Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2006.285.288AtilHulya 2200692A total of 2133 normal lactation records of Holstein Friesian cows raised at five herds in Turkey, during the period from 1982 to 1998 were used in this study to estimate phenotypic and genetic parameters for 305 day milk yield (305 dMY), Lactation Period (LP) and Age at First Calving (AFC). In addition, four selection indices were constructed by using one standard deviation as a relative economic weight. Least squares analysis showed significant effects of herds, sire within herds, year and moth of calving on all traits studied (p<0.01), except the effect of year and month of calving on LP. Heritability estimates were 0.47, 0.18 and 0.53 for 305 dMY, LP and AFC, respectively. Genetic and phenotypic correlations among 305 dMY and LP were positive and highly significant, while, other correlations were small. Four selection indices were constructed, index I1 incorporating 305 dMY, LP and AFC was the best (RIH = 0.77) and it is recommended if the selection was exercised at the end of the first lactation. In addition, using one standard deviation as relative economic values is easy in estimation and small differences between this method and actual economic values.]]>Abubaker, B.Y., E.E. McDowell, K.E. Wellington and L.D. van Vleck,19866910811087Atay, O., S.M. Yener, G. Bakir and A. Kaygisiz,199519441447Atil, H. and A.S. Khattab,200043115122Atil, H., A.S. Khattab and Y. Gevrekci,200527117120Basu, S.B., D.S. Bhatnagar and V.K. Taneja,198252279283Bakir, G. and B. Sogut,1999Cunningham, E.P.,1972El-Awady, H.G., M.N. El-Arian and A.S. Khattab,20022782058205El-Khidir, H.A.A., P.M. Hhalifa, A. Khalaf and E.S.E. Gaili,197996210217El-Arian, M.N., H.G. El-Awady and A.S. Khattab,20034099109Falconer, D.S. and T.F.C. Mackay,19964th Edn.,Pages: 464Pages: 464Hazel, L.N. and J.L. Lush,194233393399Hazel, L.N.,194328476490Henderson, C.R.,19539226252Henderson, C.R.,1963982141163Harvey, W.R.,1990Hussein, A.M.,20042004Khattab, A.S. and Z.A. Sultan,1991108349354Khattab, A.S., H.G. El-Awady, M.N. El-Arian and A. Mourad,2003401526Makuza, S.M. and B.T. McDaniel,199679702709Swiger, L.A., W.R. Harvey, D.O. Everson and K.E. Gergory,196420818826Tabler, K.A. and R.W. Touchberry,19553811551163