Different CO2 levels during incubation interact with hatching time and ascites susceptibility in two broiler lines selected for different growth rate

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Abstract
Embryos from ascites sensitive (AS) and resistant lines (AR) were subjected during the third week of incubation to a high CO2 (0.4%) (HC) or normal CO2 level of 0.2% (NC) in the incubators. The effect on embryonic and hatching parameters and growth, ascites sensitivity and related physiological parameters was followed. At NC conditions AR embryos hatch earlier than AS ones but this difference completely disappeared under HC condition, since hatching time of the AS line was reduced. Moreover, AS embryos showed slightly lower T4 and T3 levels than AR embryos. Embryos of both lines incubated at HC had higher plasma T3 concentrations than those incubated at NC. Chickens that had been incubated at HC level showed less ascites mortality than those incubated at NC. RV/TV ratios were higher in NC birds compared with HC ones. It is concluded that different ventilation levels during incubation interact with total incubation time and thereby influence ascites susceptibility.