Effects of drilling holes into the air cell of incubated goose eggs on distribution of oxygen partial pressures under the shell

1. The purpose of this work was to measure changes in oxygen pressure in the air cell and under the eggshell (P_AO₂) of pre-pipping goose eggs before and after drilling holes into the air cell. 2. Drilling a 0.6 mm² (diameter of 0.9 mm) hole into the air cell caused an increase in air cell P_AO₂ of about 10 Torr. The rate of increase attenuated as hole area increased and reached about 21 Torr when the drilled area was 8.5 mm². 3. The P_AO₂ of intact eggs was not equally distributed under the shell. It was high in the air cell area (108 Torr) and decreased towards the pointed end (86 Torr). 4. The increase in P_AO₂ after drilling a 4.9 mm² hole was high in the air cell (18 Torr) and decreased with distance, becoming non-significant at the pointed end. The significant increase in P_AO₂ after drilling was limited to a distance of up to 38 mm along the shell from the edge of the air cell. This indicates that lateral diffusion in the shell membranes under the shell is limited. 5. Drilling a hole of 3.5 to 4.9 mm² was enough to increase air cell P_AO₂ in most of the eggs above the critical value of 100 Torr for hatching success. The increase in P_AO₂ was limited to about half the area of the shell and the average increase in P_AO₂ was 6.3 Torr (equivalent to a 0.9% increase in ambient O₂). However, the blood perfusing chorioallantoic areas further away from the air cell edge may not be fully saturated with O₂ and may not be sufficient to compensate fully for the low O₂ availability caused by low eggshell conductance.