Hypoxic incubation blunts the development of thermogenesis in chicken embryos and hatchlings

Department of Physiology, McGill University, Montreal, Quebec, Canada Submitted 20 December 2006 ; accepted in final form 6 March 2007 We asked to what extent sustained hypoxia during embryonic growth might interfere with the normal development of thermogenesis. White Leghorn chicken eggs were incubated at 38°C either in normoxia (Nx, 21% O 2 ) or in hypoxia [Hx, 15% O 2 , from embryonic day 5 (E5) until hatching]. The Hx embryos had lower body weight (W) throughout incubation, and hatching was delayed by about 10 h. For both groups, all measurements were conducted in normoxia. At embryonic day E11, the static temperature-oxygen consumption (ambient T- O 2 ) curve was typically ectothermic (Q 10 = 1.92–1.94) and similar between Nx and Hx. Toward the end of incubation (E20), the Q 10 averaged 1.41 ± 0.06 in Nx and 1.79 ± 0.08 in Hx ( P < 0.005), indicating that the onset of the thermogenic response in Hx lagged behind Nx. In the 1-day-old hatchlings (H1), body weight did not significantly differ between Nx and Hx. At H1, the T- O 2 curves were endothermic-type, and more so in the older (>8 h old) than in the newly hatched (