Shell characteristics of eggs laid at 2,800 M by hens transported from sea level 24 hours after hatching

No significant differences in eggshell conductance and permeability to gases, pore area, shell thickness, or egg mass were found when eggs laid by hens transported to 2,800 m as 1‐day‐old chicks were compared to eggs laid by the parental stock at sea level. These results fail to confirm findings of Rahn et al. ('82) which suggested that alterations of eggshell structure could be associated with changes in barometric pressure. The conductance to gases (G) of the avian eggshell is a function of the sizes and numbers of pores through the shell (Ap) and shell thickness (L) (Ar et al., '74). The average values of Ap and L characteristic of each species are thought to result from rigorous natural selection, since they control the rates of gaseous exchange between the embryo and its environment and influence its survival to hatching (Ar and Rahn, '80). The average conductance to water vapor (G H 2O) of eggs laid by montane populations of wild birds and acclimatized domestic fowl is significantly decreased below sea level values in approximate proportion to the decreased in barometric pressure (P_B) at each collecting location (Wangensteen et al., '74; Rahn et al., '77; Carey et al., '83; Leon‐Velarde et al., '84). The decreased conductance is considered to be important for embryonic survival at high altitude since it appears to offset the increased tendency of water vapor to diffuse from the egg at low P_B and to result in rates of water loss that are independent of P_B in at least one species (Carey et al., '83).