Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.1999.1178.1183KhattabA. S.AtilH.4199924A total 1481 first lactation records of local born Friesian heifers were collected from Sakha Farm, Animal Production Research Institue, Ministry of Agriculture, during the period from 1980 to 1993. A linear mixed model was used to study the fixed effects of month and year of calving, age at first calving as a covariate and the random effect of sire on productive traits (i.e., 90 day milk yield (90dMY), 305 day milk yield (305dMY), total milk yield (TMY), lactation period (LP) and dry period (DP)). The effects of the same factors on reproductive traits (i.e., days open (DO) and calving interval (CI)) were also studied. Least squares means of 90 dMY, 305 dMY, TMY, LP, DP, DO and CI were 959 kg, 3252 kg, 3709 kg, 367 d, 65 d, 145d and 426d, respectively. A least squares analysis of variance showed significant effect of month of calving on 90 dMY, 305 dMY, TMY and LP (p<0.05 or p<0.01). Year of calving had a significant effect on all traits studied (p<0.05 or p<0.01). Including age at first calving (AFC) as a polynomial regression of the second degree in the model yielded significant (p<0.05 or p<0.01) partial linear regression coefficients of 90 dMY, 305dMY, TMY and DP on AFC while the quadratic term was significantly only for 305dMY. Sire of the heifers had a significant effect on all productive traits. Heritability estimates for 90dMY, 305dMY, TMY, LP, DP, DO and CI were 0.30 ± 0.08, 0.30 ± 0.08, 0.15 ± 0.06, 0.10±0.06, 0.09±0.06, 0.05±0.06, 0.05±0.06, respectively. In addition, genetic and phenotypic correlations between different traits studied are calculated and tabulated. Negative genetic correlations between each of DP, DO and CI and 90dMY, 305dMY and TMY concluded that selection against dry period and days open will increase milk yield. Therefore, a reduction of DP and DO are the desirable goal of dairymen.]]>Abdel-Bary, H.H., M.M Mahmoud, H.I. Zaky and A.A. Mohamed,1992Abdel Glil, M.F.,1996Ali, A., Z. Ahmad, G. Mohiuddin and K. Javed,1999Ashmawy, A.A. and S.A. Mokter,1984Ashmawy, A.A., F.A. Khalil and A.S. Khattab,1986Atay, O., S.M. Yener, G. Bakir and A. Kaygisiz,1995Bagnato, A. and P.A. Oltenacu,1993Basu, S.B. and A.S. Ghai,1980Berger, P.J., R.D. Shanks, A.E. Freeman and R.C. Laben,1981Britt, J.H.,1975El-Awady, H.G.,1998EI-Fouly, M.A., E.A. Kotby and H.E. El-Sobhy,1976El-Nady, S.S.,1996El-Sedafy, E.R.M.,1989Eltawil, E.A., S.A. Moukhtar, E.S. Galal and E.S. Khishin,1976Everett, F.W., D.V. Armstrong and L.J. Boyd,1966Gad, M.,1995Gill, G.S. and F.R. Allaire,1976Hansen, L.B., A.E. Freeman and P.J. Berger,1983Harvey, W.R.,1987Hussen, A.,1996Janson, L.,1980Kafidi, N., P. Leroy, C. Michaux and A. Francois,1992Kaya, I.,1996Kaygisiz, A.,1997Khalil, M.H., M.F.A. Glil and M.K. Hamed,1994Khalil, M.H., E.A. Afifi, L.H. Bedir and Z.M. Zediari,1992Khattab, A.S.,1992Khattab, A.S. and A.A. Ashmawy, 1988Khattab, A.S., M.M. Mabrouk and A.M. El-Hakim,1987Khattab, A.S. and Z.A. Sultan,1991Kornel, D. and B.N. Patro,1988Kragelund, K., J. Hillel and D. Kalay,1979Lefton, V. and S.C. Patina,1995Malau-Aduli, A.E.O., B.Y. Abubakar, O.W. Ehoche and N.I. Dim,1996Mansour, H.,1992Metry, G.H., J.C. Wilk, R.E. McDowell and H.A. El-Rigalaty,1994Olds, D., T. Cooper and F.A. Thrift,1979Onenec, A.,1997Ragab, M.T., A.S. Abdel Aziz and H.M. Morad,1973Rege, J.E.O.,1991Sallam, M.T., F.M. El-Feel and A.S. Khattab,1990Schaefer, L.R. and C.R. Henderson, 1972Seykora, A.J. and B.T. McDaniel,1983Sharma, J.M., M.M. Dhingra and B.S. Gurung,1987Smith, J.W. and J.E. Legates,1962Soliman, A.M. and M.K. Hamed,1994Swalve, H. and L.D. van Vleck,1987Swiger, L.A., W.R. Harvey, D.O. Everson and K.E. Gergory,1964Afifi, E.A., M.H. Khalil and M.A. Salem,1992