Abstract
1. Eggs from two layer-type breeder flocks (ISA-W vs Leghorn) between 30 and 45 weeks of age were used in 4 trials to study the effects of lighted incubation on embryonic growth from 5 to 18 d of age and hatchability per cent (HP). The physical dimensions, eggshell characteristics and conductance (EC) of eggs of the two strains were compared. 2. Eggs were set in an incubator on trays either in the dark-control or under two tubes of 20-watt white fluorescent light during the first 18 d of incubation. The light intensity ranged from 1230 to 1790 lux at the surface of the eggs. Eggs were transferred to dark hatching compartments at d 19 of incubation. 3. The genetic make-up of birds influenced the physical dimensions and eggshell characteristics of eggs. ISA-W eggs had higher weight, surface area (ESA), volume (EV), width, EC, shell volume and HP, and lower ESA:EV ratio, per cent shell, shell density and dead embryos than those of Leghorn eggs. 4. Lighted incubation increased daily embryonic growth (mg/d) and HP by 3.9 and 5.9%, respectively, when compared with the dark-control incubation. 5. The physical dimensions and eggshell characteristics of eggs influenced the effects of lighted incubation on embryonic growth and HP. Lighted incubation increased embryonic growth and HP of ISA-W eggs. The increase in embryonic growth and HP of the Leghorn eggs was not significant. 6. The genetic make-up of birds influenced the physical dimensions and eggshell characteristics of their eggs and these differences in the characteristics of hatching eggs influenced embryonic growth and HP when incubated under light.