Adverse effect of failure to turn the avian egg on the embryo oxygen exchange

Fertile chicken eggs belonging to the same flock of hens were divided into two groups and incubated for 16 days. During incubation, group 1 eggs were turned twice a day and group 2 eggs were left unturned. Blood sampled from the allantoic vein or artery was analyzed for gas tensions (PO2 and PCO2), pH and Hct. These values were compared by unmpaired t-test for significance differences between the two groups. While the differences of PCO2 and pH were found insignificant, failure to turn the eggs caused a pronounced fall in the arterialized PO2 which was accompanied with an increase in Hct. In addition, the embryo weight was reduced in unturned eggs. Lack of turning retarded the absorption of albumen. The unabsorbed albumen interposed between the chorioallantoic membrane and inner shell membrane, impeding the blood oxygenation through the chorioallantois. Little change in PCO2 might be attributed to a large diffusive conductance of the chorioallantois for CO2. The present results suggest that the eggs must be turned periodically during incubation to prevent the distortion of normal oxygen exchange especially for the study of egg respiration.