For local eggs or eggs laid at a similar altitude? Nothing. The porosity of the eggshell is adapted to the lower partial pressure of oxygen available, so they hatch just fine. ( I have a Brinsea with the humidity pump)What do you do different in high altitudes?
For eggs shipped from a low altitude, I up the humidity a bit to help the oxygen cross, but without oxygen to pipe in near the end there's not much you can do. Some people have used CO2 scrubbers, but the effectiveness is mixed. Eggs shipped from sea level I'm lucky to get 1 or 2 to hatch out of 2 dozen.




