Abstract: Total of 1902 first lactation records of imported and locally born Friesian heifers were collected during the period from 1980 to 1993. A linear mixed model was used to study the random effect of sire, fixed effects of farm, origin of cow, year and month of calving and both age at first calving (AFC) and days open (DO) as covariate on some productive traits, i.e. annualized milk yield (AMY), Total milk yield (TMY), 305 day milk yield (305-DMY) and dry period (DP). The effects of the same factors (except DO was replaced by TMY as covariate) on two reproductive traits, i.e., DO and calving interval (CI) were also studied. Sire transmitting ability (ETA) on the basis of Best Linear Unbiased Prediction method (BLUP) as well as rank correlation coefficients among ETA’s obtained for the different traits were also estimated. Least squares means of AMY, TMY, 305-DMY, DP, DO and CI were 2886, 3210, 2995 kg, 79.3, 141 and 422 days, respectively. Least squares analysis of variance showed that sire of the heifers had a significant effect on all traits except DP and CI. Farm showed significant effect on all studied traits, while origin of cow had non-significant effect. Year of calving had a significant effect on AMY, TMY and 305-DMY, while it had non-significant effect on DP, DO and CI. Month of calving had a significant effect on AMY, TMY, 305-DMY, DO and CI while, it had non significant effect on DP. Age at first calving (AFC) yielded insignificant partial linear and quadratic regression coefficients for all traits. While, DO and TMY as yielded highly significant partial linear regression coefficients of all productive or reproductive studied traits. The quadratic term was significant for dry period (DP) on DO and for DO and CI on TMY.
Heritability estimates for AMY, TMY, 305-DMY, DP, DO and CI were 0.304, 0.300, 0.316, 0.036, 0.190 and 0.170, respectively. Negative genetic, phenotypic and environmental correlations between DP and each AMY, TMY and 305-DMY concluded that selection against dry period would increase milk yield. Estimates of ETA’s ranged from –159.1 to 277.6, –191.0 to 266.0, –184.4 to 289.2 kg and –29.7 to 32.3 d for AMY, TMY and 305-DMY and DO, respectively. Percentage of sires that had negative ETA’s for above traits were 58.8, 52.9, 55.9 and 55.9, respectively. Sires that showed positive values for TMY, had positive values for the other traits. The rank correlation coefficients among productive traits were high and positive. Meanwhile, the rank correlation coefficients among ETA’s for DO and each of AMY, TMY and 305-DMY were negative.