Abstract: The present experiment was conducted at the Poultry Research Center (Department of Poultry Production) Faculty of Agriculture Alexandria University during three successive seasons (1993, 1994 and 1995). In order to study the direct response to selection for age at sexual maturity on Alexandria crossbred chickens and its correlated response on body weight at four, eight and twelve weeks of age, fertility, hatchability and viability, and the reproductive traits including, body weight at sexual maturity, egg number, egg weight and egg mass during the first 90 days of laying. Moreover, calculation some genetic parameters like the heritability and phenotypic correlations between studied traits
Two populations were used, (selected and control). The females which reached maturity age earlier than the population mean were selection, while the selection in males was dove based on their heavier eight weeks body weight and according to full and half sister age at sexual
maturity, these selected males and females was considered as selected parents.
Random mating was used during the two generations in the control population.
The results were discussed and the main conclusion can be summarized in the following.
1- The means of age at sexual maturity for the base, first and second generation were 173.18, 165.80 and 155.1 days for the selected line, and 175.02, 173.31 and 176.73 days for the control line, respectively. The difference between the all source of variance were significant.
2- The selection differential values for age at sexual maturity by generation were -7.07 , -8.63 and -10.49 days and its selection intensity were 0.41,0.78 and 1.45.
3- The overall means of fertility percentage were 95.78% and 96.28% for the selected and control lines, respectively, while the hatchability percentage were 69.55% and 72.36% for the selected and control lines, respectively.
4- The overall mean of viability percentage were 80.67% and 86.22% in the first generation at 8 weeks of age for the selected population and control line and 50.42%, 55.18% in the second generation, for the selected and control population, respectively.
5- Selection for age at sexual maturity, resulted in a considerable increases for body weight-at eight weeks of age equal to 6.84 gm for males, while decreased body weight of females by 11.85 gm. At twelve weeks of age the body weight of males increased 39.77 gm but decreased 22.64 gm in females.
6- Selection for age at sexual maturity increases egg number, egg weight and egg mass by 12.48 egg, 0.16 gm and 483.2 gm, respectively. While decreased body weight at sexual maturity 1.96 gm.
7 - Heritability estimates of age at sexual maturity in base generation were 0.39, 0.00 and 0.15 based on sire, dam and sire plus dam component of variance, respectively. 0.26, 1.00 and 0.66 in the base and first generation. While in second generation was 0.28 based on sir components of variance only.
8- Heritability estimates for body weight at eight weeks of age were 0.00, 0.51 and 0.15 and 0.32, 0.08 and 0.2 in the first generation for males and
females based on sir, dam and sir-plus-dam, respectively. In second generation the heritability estimates were 0.47 and 0.45 for males and females, respectively on sir components of variance only.
9- Heritability estimates for body weight at sexual maturity in base generation were 0.00, 0.12 and 0.08 based on sir, dam and sir- plus-dam, respectively, the corresponding values were 0.00, 0.52, 0.18 in the first. generation, \vhile in th~ second generation was 0.37 on sir components of variance only.
10- Heritability estimates for egg number in base generation were 0.5, 0.00 and 0.1 based on sir, dam and sir-plus-dam, respectively, the corresponding values were 0.06, 0.3 and 0.18 in the first generation, while in the second generation was 0.16 on sir components of variance only.
11- Heritability estimates for egg weight in base generation were 0.16, 0.79 and 0.48 based on sir, dam and sir-plus-dam, respectively, the corresponding values were 0.08, 0.59, 0.33 in the first generation, however in the second generation was 0.09 on sir components of variance only.
12- Heritability estimates for egg mass in base generation were 0.39, 0.00 and 0.08 based on sir, dam and sir-plus-dam, respectively. The corresponding values were 0.12, 0.21, 0.16, however in the second generation, however in the second generation was 0.09 on sir components of variance only.
13- The phenotypic correlation between age at sexual maturity and reproductive traits resulted in the negative correlation with egg number and egg mass, while the positive correlation with egg weight and body weight at sexual maturity.
14- It could be concluded from the results of the present study that selection for age at sexual maturity increased egg number and egg mass.
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