ملخص
Abstract The present study was carried out to estimate genetic parameters associated with direct and maternal genetic effects on birth and weaning weights in Friesian herd and to estimate the prediction of breeding values for both traits, by using bivariate repeatability animal model. The data used in the study included pedigree and weight records of calves born between 1984 and 2014. Overall means of birth weights B.Wt and weaning weight W.Wt were 37.66 ± 0.08 and 64.02 ± 0.75kg respectively; the average of suckling period (SP) was 61.62± 3.44 days of age. The person correlation coefficient between birth weight and weaning weight was 0.312, considering that the duration of suckling introduced as partial variable. The results showed that the year and season of birth had high significant effect on calf birth weight and weaning weight (P <0.0001) in addition the influence of) of sex of calf and dam parity on calf birth weight was highly significant (P<0.0001). Direct heritability estimates for birth weight B.Wt and weaning weight W.Wt are 0.33 and 0.12, respectively, while, maternal heritability estimates for the same traits are 0.12 and 0.08, respectively. Total heritability estimates are 0.24 and 0.07 for B.Wt and W.Wt, respectively. Repeatability estimates are 0.41 and 0.22 for B.Wt and W.Wt, respectively. Phenotypic and genetic correlations between the traits are 0.38 and 0.80, respectively. Values of Estimated breeding values ranged from -5.43 to 7.73 kg for B.Wt and ranged from -2.54 to 2.75 kg for W.Wt. It concluded that the direct and maternal heritability and direct and maternal correlation coefficients for birth and weaning weights were moderate to low, the additive genetic variation for traits was deemed sufficient to allow effective selection for growth performance