Four synthetic strains of chickens, including Matrouh (MT), Mandarah (MN), Silver Montazah (SM) and Inshas (IN), were used in a crossbreeding experiment for four years to estimate direct additive genetic effects ( ), maternal effects ( ), direct heterosis ( ) and maternal heterosis ( ) for age and weight of hen at the first egg, weight of the first egg, egg number and mass for the first 10 eggs, egg number and mass during 90 and 120 days of egg production, egg number and mass for two days per week of production, egg number and mass for one week per month of production and clutch sizes and pause durations during 90 and 120 days of egg production. The egg production traits were recorded for a total of 747 sexually mature hens belonging to the different genetic groups. A total of 34 sires and 230 dams from MT chickens, 32 sires and 199 dams from MN chickens were used to produce 2894 chicks of the parental generation of MN and MT. In crossbreeding generations, two-way crossbreds (653 chicks of ½MN½MT and ½MT½MN) and three-way crossbreds (809 chicks of ½IN¼MN¼MT and ½SM¼MT¼MN) were produced. The estimates of  on all egg traits studied were significantly in favour of MN strain (P≤0.01). Also, the estimates of  were significantly in favour of MN dams for age at first egg, most egg production traits and clutch sizes, while the estimates for pause durations were in favor of MT dams. Estimates of  were significant with favorable heterotic rates ranging from 3.8 to 28.5 % for maturity of hen at the first egg, 19.7 to 29.3 % for egg production and 3.2 to 36.1 % for partial egg recording (P≤0.05 or P≤0.01). The percentages of  were favorably positive for all clutch sizes (ranging from 13.1 to 57.4 %; P≤0.01), while they were favorably negative for all pause durations (ranging from -17.3 to -44.2 %; P≤0.01). The percentages of  were favorable with heterotic rate of -2.6 % for age at the first egg (P≤0.05) and 7.8 to 8.2 % for egg production (P≤0.01). The heterotic maternity was favorably positive and ranging from 3.2 to 10.5 % for four traits of partial egg recording (P≤0.05) and 4.6 to 15.5 % for most clutch sizes (P≤0.05 or P≤0.01), while they were favorably negative for all pause durations (-5.0 to -31.8 %; P≤ 0.05 or ≤ 0.01).