Thermoregulation in precocial avian embryos

Abstract

Oxygen consumption was measured and heat production (HP) calculated in Muscovy Duck (Cairina moschata) and Domestic Fowl (Gallus gallusf domestica) embryos at different ambient temperatures (Ta) using a closed (Scholander-method) or a halfopen system connected to a paramagnetic oxygen analyzer (Magnos, Hartmann and Braun, Germany) . After internal pipping, respiratory rate, respiratory tidal volume and minute volume as well as blood flow in the chorioallantoic membrane were estimated in a number of embryos at 40°C. Simultaneously, the temperature of the allantoic fluid (Taf) and colonic temperature (Tc) were measured . In other experiments, Muscovy Duck embryos were incubated at Ta of 34.5 ° C and HP was compared at different Ta with that of birds incubated at 37.5 °C. Generally, a decrease in Ta led to a decrease in Tc, Taf and HP. The estimated HP is the result ofthe depressing influence of the Q10 -effect and the positive influence of CNS-controlled thermoregulatory HP. The older the embryo, the lower the minimal Q10 obtained, the lower the threshold Taf for a Q10 of 2.0 and the higher the Taf at the minimal Q10. The results suggest that endothermic reactions in precocial birds occur very early during embryonic development . Prenatal temperature experiences seem to stimulate thermoregulatory HP of embryos. During the period between internal and external pipping, panting occurred with increasing body temperature and, in Muscovy Duck embryos, the respiratory rate increased in the Tc-zone between 38.5 and 40 .5 °C. It seems to be that many organ functions occur during embryonic development, before these functions are ultimately necessary to ensure the survival of the embryo . Prenatal activation of functional systems may have a training effect on the postnatal efficiency of the related adaptive mechanisms.