Effects of interaction of incubator CO2 levels and mixing hatching eggs of different embryo growth trajectory on embryo physiological and hatching parameters.

1. Two experiments were designed to investigate the effects of mixing eggs of different genotype and incubating with different CO2 concentrations on embryonic parameters. Half of the eggs were incubated in a CO2 controlled incubator (VCO2) during the first 10 d of incubation and the other half was incubated at standard incubation ventilation rate (SV). 2. From 10 to 18 d of incubation, thick albumen and embryos were weighed. Blood samples were collected at d 18 of incubation, at internal pipping and at hatch for determination of triiodothyronine (T3), thyroxine (T4) and corticosterone concentration. During the last 2 d of incubation, hatching events of individual eggs were monitored every 2 h. 3. From 4 to 5 d of incubation in the SV group of Experiment 1, pH values of Ross strain chickens were lower than those of Isa Brown. From d 12 of incubation onwards, Ross embryos grew faster than those of Isa Brown. At 14 and 16 d of incubation, Ross eggs in the CO2 controlled incubator had lower albumen weights compared to all other treatments. 4. T3 concentrations in Ross embryos were higher than those of Isa Brown embryos. Chicken weight at hatch was in the following order: Isa Brown SV < Isa Brown VCO2 = Ross SV < Ross VCO2. 5. In Experiment 2, incubation time of VCO2 eggs until internal pipping, external pipping and hatch was significantly shorter than that of SV eggs. 6. It was concluded that mixing of hatching eggs of differential embryo developmental trajectory affects their hatching process.