الفهرس 
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Abstract
The main objectives of this study were to estimate genetic and nongenetic factors affecting productive and reproductive traits in dairy cattle. As well as estimate genetic and phenotypic parameters for these traits, and to compare some productive and reproductive traits of the imported Friesian heifers and their progeny locallyborn heifers under the conditions of Damietta Province located at the eastern north part of the Nile Delta in Egypt. Fainally to compare two statistical programs. The first statistical program was linear mixed model least squares and maximum likelihood (LSMLMW) computer program of Harvey (1990). The second statistical program was Multivariate Derivative Free Restricted Maximum Likelihood (MTDFREML) of Boldman et al. (1995) to estimate the genetic parameters for the same traits analyzed by Harvey (1990) program using the same statistical models. Two models of statistical analysis were used for studying factors affecting some productive and reproductive traits mentioned above as well as estimation of genetic parameters of these traits using the same program. These results may lead to the conclusion that improving management and selecting the region in which a certain foreign breed would be kept are very important. It worth to mention that this comparison between imported and locally born cows will be more accurate if the sensitivity to disease as well as longevity traits taken into account when comparing. So that further studies must be carried out including these two important factors. On another topic, the significant effect of sire on milk production traits (i.e. TMY, 305DMY and DMY) beside the moderate to high values of heritability estimates of these traits (0.22 to 0.34) indicate to the possibility of making genetic improvement in these traits through sire selection. The differences in heritability estimates between Harvey program and Animal model reflect the importance of using the more accurate and practical model in estimation the phenotypic and genetic parameters when design and optimizing breeding schemes. Key words: ( not more than Ten) : Fresian , genetic parameters, heritability, single trait animal model , milk yield traits.