OXYGEN AND AVIAN EGGSHELL FORMATION AT HIGH-ALTITUDE

Many birds at high altitude lay eggs with reduced eggshell diffusive c onductance to water vapor. Disagreement exists about the cause, but hy potheses include physiological acclimatization and genetic adaptation. To investigate this, we tested for the occurrence of physiological ac climatization and quantified the effect of relieving hypoxia at high a ltitude. Ten laying hens (Gallus domesticus) were exposed to elevation s of 3800 m (PI(O2) 90 Torr), 3800 m with supplementary oxygen (PI(O2) 140 Torr), and 1200 m (PI(O2) 125 Torr). 573 eggs were collected and analyzed during the 17-week experiment. Shell conductance, aggregate p ore area, and shell thickness were reduced at 3800 m compared to 1200 m or 3800 m with supplementary oxygen. There was a lag in the response to changes in altitude or PI(O2) that corresponded to a time constant of approximately 2.5 weeks. We conclude that physiological acclimatiz ation of eggshell conductance occurs in some chickens, and that it is probably stimulated by hypoxia.