A total number of 1920 eggs were incubated from two strains of chickens at the 28th, 40th and 52th weeks of age .Hens were artificially inseminated twice a week throughout the experimental period. Eggs were randomly assigned to four treatments according to vitamin D3 supplementation (0, 300, 600 or 1200 IU/kg of ration) for El-Mamourah as well as Sinai strains in each interval. Each treatment was assembled to three replicates 80 eggs each. The objective of this study was to investigate the effect of adding graded cholecalciferol levels (vitamin D3) to the layers diets on reproductive performance in both Mamourah (M) and Sinai (S) strains at different production periods.
The obtained results can be summarized as follows:
1- M eggs had significantly heavier egg weight loss percentage (11.51 %) during the whole period of incubation (0_18 days) than those of S ones (11.09 %).
2-Results indicated that increasing the cholecalciferol content in diet cursed increasing rate of egg weight loss during the whole period of incubation .
3-Results obtained showed that a reduction in egg weight loss percentage by advancing in age interval.
4- Egg fertility and hatchability in M strain was higher than those of S ones
5- Hens of both strains that fed the highest and the lowest levels of cholecalciferol had the highest and the lowest hatchability and the lowest and highest embryonic mortality, respectively.
6- It was noticed that hatchability (%) of all set or fertile eggs decreased in eggs laid early in a cycle (80.95 and 84.70 %), thereafter, it significantly increased reached its maximum value in eggs laid middle laying cycle (85.37 and 88.90 %) then hatchability (%) of all set eggs significantly decreased in eggs laid late laying cycle (82.03 %), whereas, hatchability (%) of fertile eggs slightly decreased in eggs laid in the same interval (88.28 %).
7- The results indicated that level of vitamin D3 supplementation in the maternal diet was effective in improving absolute and relative (%) body weights of the progeny.
8- The significantly higher of economic efficiency (%) throughout the experiment was observed in chicks hatched from M eggs than those S ones by about (22.8 %). This improvement of economic efficiency may be due to increase of hatchability of M eggs as well as price of one M chick as compared to S ones. In addition to the previous mentioned discussion, the economic efficiency (%) responded positively to the increasing of levels of vitamin D3 in maternal diets from 300 up to 1200 IU/kg feed and surpassed than those of the control group by about 17.6, 36.6, and 39.1 %, respectively