الفهرس 
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Abstract
This study was carried out to evaluatethe non-genetic factors that affecting milk production traits, estimate genetic parameters and to predict breeding value for milk traits in dairy cattle. Moreover, to reveal the PRL and FSHR gene polymorphisms, and to detect the association between 305-DMY andPRLas well as DO and FSHR polymorphisms using PCR- RFLP technique. Eighty six blood samples (44 samples for prolactin gene and 42 samples for FSHR gene) were collected from Holstein cattle based on EBVs of the animals. Blood samples for DNA extraction were collected from tail vein by venuject tube containing EDTA and stored at – 20oC.The results were summarized as follow : Parity hada significant effect (P < 0.05) on PMY, TPMYand305-DMY. Season of calving had no significant effect (P >0.05) on both PMY and 305-DMY. However, it had a significant effect on TPMY.Year of calving had a significant effect (P < 0.05) on each of PMY, TPMY and 305- DMY. Days open had a significant effect (P < 0.05) on both 305- DMY and time to attain peak milk yield (TPMY). However, it had no significant effect (P > 0.05) on PMY.Higher ranges, standard errors of EBVs indicated the existence of more genetic variation among individuals thus increase the possibility of selection for these traits, which reduce bias from selection that achieve the best accuracy of predictions and rapid genetic improvement. AB genotype of PRL polymorphism in Holstein breed had significantly higher average of 305-DMY than AA genotype in high producing cows. Prolactin genotype at an early animal’s age represents an advantage as this hormone is a good candidate to be considered in program of marker assisted selection as it shortens the interval between generations. Reproductive performance has been found to deteriorate as milk yield increased due to antagonistic unfavorable genetic correlation between milk production and fertility traits. AA genotype of FSH receptor can be considered a potential marker for reproduction traits in Holstein cattle at an early animal’s age.