Struthio camelus embryo

̇ ̇ Ž . Ž . We measured oxygen consumption V and carbon dioxide emission V rates, air-cell gas partial pressures of O CO 2 2 Ž . Ž . Ž oxygen P O and CO P CO , eggshell water vapour conductance and energy content of the ostrich Struthio A 2 2 A 2 ̇ . Ž . camelus egg, ‘true hatchling’ and residual yolk, and calculated RQ and total oxygen consumption V for ostrich O tot 2 ̇ eggs incubated at 36.5 C and 25% relative humidity. The V pattern showed a drop of approximately 5% before O2 ̇ internal pipping. V just prior to internal pipping agrees with allometric calculations. Despite the higher incubation O2 ̇ 1 Ž . Ž . temperature compared to other studies, and the resultant shorter incubation duration 42 days , V 91.7 l kg was O tot 2 Ž . similar to a previously reported value. RQ values during the second half of incubation approx. 0.68 were lower than Ž . expected for lipid catabolism. Prior to internal pipping, P O and P CO were 98 and 48.3 torr 13.1 and 6.4 kPa , A 2 A 2 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. 2001 Elsevier Science Inc. All rights reserved.