Data of three up-grading trials of local Domiati cattle with Friesian (Friesian trial ). Dairy Shorthorn (Shorthorn trial), and Jersey (Jersey trial) were used to quantify the importance of direct additive effect (G1), maternal additive effect (GM), direct herterosis (HI), maternal heterosis (HM), direct recombination effect (RI) and maternal recombination effect (RM) for birth weight of calves. In the three trials, cow breed group effect was significant (P<0.05 or 0.001) on birth weight of their calves. Means of birth weight increased with the increase of Friesian (F) blood in the cow form ½ to 7/8 F and Shorthorn (S) blood from ½ to ¾ S but decreased with the increase of Jersey (J) blood from ½ to 15/16 J. Estimates of individual additive effects (GI) in Friesian and Shorthorn trials were significant (P<0.001), large and in favour of the European breed. Direct heterotic superiority (HI) of crossbred cows were evidenced over their purebred parental breed groups. Estimates of HM percentages were 4.1, 5.1 and 5.1% in Friesian, Shorthorn and Jersey trials, respectively. Positive and significant (P<0.05 or P<0.001) estimates of RI was significant (P<0.001) only in Friesian trial. Keywords: dairy cattle, Egypt, birth weight, additive, heterotic and recombination effects.