Comparative physiological study on environmental temperature effect influencing development of thermoregulatory competence in birds.

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1.Development of respiratory sinus arrhythmia and heart rate circadian rhythms in chickens.Simultaneous measurements of respiratory activities and instantaneous heart rate (IHR) in externally pipped (EP) embryos which switch gas exchanger from the chorioallantois to the lung and also in newly hatched chicks evidenced development of respiratory sinus arrhythmia in chickens. In addition, long-term measurement of IHR during a week post-hatch elucidated development of heart rate (HR) circadian rhythms in chickens. In ducks and emu, HR circadian rhythms were not evident as compared with chickens and their diurnal and nocturnal HR variations seemed to be caused by feeding or daily activities.2.Development of heart rate variability and responses to altered ambient oxygen in chicken embryos.Simultaneous measurements of embryonic HR variability both in broiler and white leghorn chickens and power spectrum analyses evidenced that development of cholinergic chronotropic control was not different between both strains. In addition, HR responses to altered ambient oxygen (hypoxia and hyperoxia) were investigated in young pre-pipped, pre-internally pipped (IP), IP and EP embryos and found to be different between pre-pipped and pipped embryos.3.Development of endothermic heart rate response in chickens, ducks and emu.In chickens, it was evidenced that sequence of exposure of hatchlings to altered ambient temperatures did not affect the endothermic HR response and brooding temperatures did not affect early development of endothermic HR response. The endothermic HR response to alteration of 10℃ in ambient temperature appeared in a day post-hatch in broiler chickens, soon after hatching in ducks and during external pipping period in emu. In addition, it was found that development of endothermic HR response was different between broiler and white leghorn chickens, which might be due to genetic selection of broiler chickens which grew fast.