An interaction between EST and CO2 was found for time until IP (P < 0.001) and time until EP (P < 0.0001; Table 1). At normal EST, time until IP and time until EP were both 5 h shorter at high CO2 compared with low CO2. No effect of CO2 on time until IP and EP was found at low and high EST. An effect of EST was found on time until hatch (P < 0.001; Table 1), at which time until hatch was longer at low EST compared with normal (∆ = 2 h) and high EST (∆ = 4 h).