Changes in eggshell water vapour conductance during shell formation in the chicken.

Time-related changes in shell porosity and eggshell water vapour conductance were measured in uterine eggs of the domestic fowl (Gallus domesticus) from 10 h in uterus to oviposition. Measurements were carried out in artificially-aborted eggs. It was found that the eggshell water vapour conductance decreased to a minimum level at 15 h in uterus. This coincided with increases in shell thickness and shell porosity as power functions of uterine time. From that time on, water vapour conductance increased as a power function of uterine time to the final value prior to oviposition. Thus, eggshell water vapour conductance is determined by different rates of dynamic changes in shell porosity and shell thickness in the course of shell calcification. The final conductance is reached about 2 h before oviposition.