Oxygen transport to avian embryo tissues occurs by three steps, two of which are driven by diffusion. This results in a series of stepwise decrements in Po2 between atmosphere and tissue. The Po2 decrements for embryos of the domestic fowl incubated at different altitudes are used here to examine potential adaptations to hypobanc hypoxia. With exposure to moderate hypoxia embryos of the domestic fowl appear to maintain adequate tissue oxygenation. Adaptive adjustments in the shell, shell membranes and chorioallantois complex were not observed. However, hemoglobin O2 affinity was increased and preliminary evidence suggests a redistribution of blood flow to maintain adequate oxygenation in higher priority areas of embryonic tissue. At severe hypoxia, embryos of the domestic fowl show decreased O2 consumption, embryo mass and lengthened incubition period. Thus at severe hypoxin the embryo of the domestic fowl does not appear to provide a realistic model. Evidence from avian embryos of species native to high altitude suggest that they are able to maintain adequate tissue oxygenation even at severe hypoxia. Preliminary evidence suggests that some of the blood vascular system and tissue level adaptations present in the chicken embryo are also present in species native to high altitude. One of these, an increase in embryonic hemoglobin-O2 affinity which is physiologically mediated in the chicken embryo is genetically-based in the embryo of the native high-altitude species.

Author notes

1From the Symposium on Physiology of the Avian Egg presented at the Annual Meeting of the American Society of Zoologists 27–30 December 1979 at Tampa Florida.