Metabolism of Avian Embryos: Ontogeny and Temperature Effects in the Ostrich

Abstract

The relation between metabolic rate and incubation age in the ostrich is different from that reported previously for the chicken, duck and herring gull. In the eggs of the ostrich a peak rate occurs 6 days before pipping and is followed by a decline of about 25%. This decline may be caused by a decrease in growth rate. The allometric relationship between the metabolic rate shortly before pipping and fresh egg mass for several species of avian eggs is parallel to but significantly below the line relating basal metabolism to body mass in adult birds. Just before hatching, an avian embryo has a metabolic rate 1/3 that of an adult bird of equal body mass. The O2 tension in the air cell shortly before pipping in the ostrich egg is considerably higher than the mean value reported for other species. There may be an allometric relationship between air cell gas tensions and fresh egg mass. The shell conductance of the ostrich egg is adapted to its relatively short incubation period but the rate of O2 consumption before internal pipping is not.