الفهرس 
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Abstract
The aim of the work was to study the effect of some of environmental factors (age at first calving, year and season of calving, parity, days open and calving interval, dry period) on milk production traits and estimation of breeding values and genetic trends. Higher milk productivity associated with lower reproductive performance which is reflected by positive phenotypic and genetic correlations among days open and total milk yield and 305-days milk yield. Wider genetic variation and this gives the chance for improving the considered trait through selection according to the superiority of the cow breeding value. Positive genetic trends for 305-DMY, AFC, fat%, fat yield and protein % indicate that there has been genetic improvement in these traits in desirable direction over the year. But negative genetic trends for DO and protein yield indicating a decrease in mean breeding value for these traits over the study period.