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Abstract
Genetic parameters for some milk production and reproductive traits were estimated in a herd of Holstein Friesian (HF) cattle in Egypt. A total of 502 lactation records of 300 HF cows sired by 29 bulls from a herd belonging to Alexandria Copenhagen Company for Dairy and Meat Production, was used in the present study. Data were collected during 7 years (2005-2011) and analyzed using SAS, XLSTAT and WOMBAT. Means of total milk yield (TMY), 305 day milk yield (305-DMY), lactation period (LP), days open (DO) and calving interval (CI) were 10718 kg, 8805 kg, 397 day, 193 day and 472 day, respectively. Parity had no significant effects on all traits, except for 305-DMY (P<0.0001). Season of calving, also had no significant effects on all traits, except for LP (P<0.0025) and DO (P<0.021). Heritability estimates of TMY, 305-DMY, LP, DO and CI were 0.19, 0.25, 0.15, 0.11 and 0.11, respectively. The moderate estimate of heritability of 305-DMY indicated that improvement in this trait could be made through selection as well as better managemental practices. Repeatability of TMY, 305-DMY, LP, DO and CI were 0.40, 0.39, 0.34, 0.25 and 0.23, respectively. Positive genetic and phenotypic correlation coefficients were obtained among all traits and ranged from 0.003 to 0.99 and from 0.12 to 0.96, respectively. except for the phenotypic correlations between 305-DMY with DO and CI which were negative (-0.01 and -0.02, respectively). Results indicated possibility of genetic improvement of milk yield by selection for 305-DMY only, due to its higher estimate of heritability, compared to TMY, and also because of its reasonably high genetic correlation with TMY