Gas Pressures in the Air Cell of the Ostrich Egg Prior to Pipping as Related to Oxygen Consumption, Eggshell Gas Conductance, and Egg Temperature

Publisher Website
Google Scholar
Abstract
It has been suggested that air cell oxygen partial pressure (PAO2) in avian eggs just prior to internal pipping (PreIp stage) resembles that of avian (and mammalian) alveolar partial pressure, e.g., PAO2 .simeq. 104 torr. On the other hand, indirect evidence from water vapor eggshell conductance (GH2O) suggests that PreIp PAO2 is allometrically related to egg mass: large and small eggs would have high and low PAO2, respectively, where the calculated PreIp PAO2 of the Ostrich (Stuthio camelus) egg, from those data, is about 125 torr. The rate of egg mass specific oxygen consumption (.ovrhdot.MO2), PAO2, and the partial pressure of CO2 in the air cell (PACO2) were measured; oxygen diffusive eggshell conductance (CO2), and air cell gas exchange ratio (R) were calculated; egg content surface temperature (Ts) and the rate of mass loss were measured in Ostrich eggs, all during the last stages of development at 35.5.degree. C and 45% relative humidity. The mass loss was corrected for the effect of R to yield rate of water loss (.ovrhdot.MH2O). This value and vapor saturation value at Ts were used to calculate GH2O. Mean .+-. standard deviation PAO2 and PACO2 during PreIp stage were 103 .+-. 4.5 torr and 46 .+-. 6.0 torr, respectively. The GO2 found (129 ml [STPD] .cntdot. (day .cntdot. torr)-1 .+-. 57) was lower than that predicted by allometric relationships or by calculation from GH2O (185 ml [STPD] .cntdot. (day .cntdot. torr)-1). The ratio GO2/GH2O was 0.59 .+-. 0.15, significantly different from the expected 0.85 (using the respective diffusion coefficients). A temperature difference of 2.0 .+-. 0.5.degree. C was measured between the egg content surface and the incubator. The higher temperature of the egg content surface, associated with an increase of water vapor pressure in the air cell, presumably decreases GO2 and increase GH2O. Values and R indicate that 1 day prior to external pipping the movements of the mature embryo influence the pattern of gas exchange by creating convective exchange.