Gas exchange and energy metabolism of the ostrich (Struthio camelus) embryo

We measured oxygen consumption (V̇_O2) and carbon dioxide emission (V̇_CO2) rates, air-cell gas partial pressures of oxygen (P_AO₂) and CO₂ (P_ACO₂), eggshell water vapour conductance and energy content of the ostrich (Struthio camelus) egg, 'true hatchling' and residual yolk, and calculated RQ and total oxygen consumption (V̇_O2tot) for ostrich eggs incubated at 36.5°C and 25% relative humidity. The V̇_O2 pattern showed a drop of approximately 5% before internal pipping. V̇_O2 just prior to internal pipping agrees with allometric calculations. Despite the higher incubation temperature compared to other studies, and the resultant shorter incubation duration (42 days), V̇_O2tot (91.7 l kg^-1) was similar to a previously reported value. RQ values during the second half of incubation (approx. 0.68) were lower than expected for lipid catabolism. Prior to internal pipping, P_AO₂ and P_ACO₂ were 98 and 48.3 torr (13.1 and 6.4 kPa), respectively. The growth pattern of the ostrich embryo is different from the typical precocial pattern, showing a time delay in the rapid growth phase. As a result, the lowered overall energy expenditure for tissue maintenance, as compared to other species, is reflected in the low yolk utilization and high residual yolk fraction of the whole hatchling dry mass. These could also result from the relatively short incubation period of the ostrich egg, thereby evading desiccation by excess water loss.