Temperature and metabolism of chick embryos and hatchlings after prolonged cooling.

Is a new quasiequilibrium state of metabolism and egg temperature reached after chick embryos and hatchlings are exposed to prolonged cooling? During the last half of the incubation period the chicken egg maintains a temperature above that of the ambient air temperature of 38 degrees C. This difference increases from about 0.2 degree C at 11 days to 2 degrees C just before hatching and to 3 degrees C by 7 days posthatching. When eggs or hatchlings are then exposed to room air at 28 degrees C, a new quasiequilibrium state is reached in 5 hr (defined as a change in egg temperature of less than 0.1 degree C X hr-1). The new difference between egg and ambient temperature varies from about 0.1 degree C at 11 days to 1.2 degrees C just before hatching, but increases in the hatchling from 6 degrees C right after hatching to 10 degrees C 5 days later. During the quasiequilibrium state at 24 degrees C the metabolic rate is maintained at about 40% of the control value up to hatching time, but thereafter rapidly increases to 70-95% by day 1. In a few cases emergence from the shell was not necessary for increases in quasiequilibrium temperature and metabolic rate.