Effects of high CO2 level during early incubation and late incubation in ovo dexamethasone injection on perinatal embryonic parameters and post-hatch growth of broilers

1.A total of 1200 Cobb broiler breeder eggs were incubated under either standard conditions (C group) or high CO2 levels (CO2 group) during the first 10 d of incubation. The CO2 level of the CO2 incubator was attained gradually by a natural build-up of CO2 due to air-tight closure of the incubator. From d 10 of incubation onwards, all eggs were incubated under standard incubation conditions. At d 18 of incubation, the eggs of both incubation groups (CO2 and C group) were either injected with water-soluble dexamethasone (DEXA group) or with saline (09% NaCl; saline group) or were not injected (control). 2.Body weights, plasma hormonal concentrations (T-3, T-4 and corticosteroid) and glucose concentrations were measured regularly during the perinatal (at IP, internal pipping) and post-hatch period (at 1, 2, 4 and 6 weeks post-hatch). Additionally, hatchability and pattern of embryonic mortality were determined after hatch. 3.The results showed that high CO2 levels during the first 10 d of incubation or dexamethasone injection at d 18 of incubation decreased embryo mortality, mainly because of a reduction in embryo malpositioning. However, a combination of a CO2 incubation and a dexamethasone injection led to an increase in embryo mortality and therefore a decrease in hatchability. 4.Although dexamethasone injection at embryonic d 18 decreased body weight in the second week of the rearing period and CO2 incubation increased body weight during the first 2 weeks of the rearing period, no consistent effect of both the incubation and injection treatments on body weight at slaughter age was observed.