KHANDOKER, A. H.*; FUKAZAWA, K; CHIBA, Y; TAZAWA, H; Muroran Institute of Technology; Muroran Institute of Technology; Muroran Institute of Technology; Muroran Institute of Technology: Estimation of homeothermal development in newly hatched chicks due to instantaneous heart rate measurement

It was previously reported that baseline of instantaneous heart rate (IHR) of newly hatched chicks was raised and oscillating with a low frequency (period of about 10-25s) by exposure to lowered temperature. An aim of this study is to elucidate the development of homeothermal response of heart rate in newly hatched chicks (day 0-3) kept at room temperature (about 23-27�C) before the measurement was made. Newly hatched chicks were exposed first to a temperature of 25�C for 1-hr period, warmed to 35�C and cooled again at 25�C and IHR was measured together with skin temperature (Ts) during warming and cooling bout. Early 0-day-old chicks responded to warming and cooling exposures with various changes in baseline HR. Some chicks increased the baseline HR during warming and decreased it during cooling. Some other 0-day-old chicks changed little the baseline HR during warming and cooling bout. In other advanced 0-day-old chicks, HR responded to warming and cooling exposures with a decrease and an increase in HR in a similar fashion as other chicks 1 to 3 days old. The diurnal variations of baseline HR during warming and cooling bout in 0-day-old hatchlings were similar to those of metabolic responses, assuring that pronounced improvement of homeothermal capacity occurs on the day hatching (day 0). On the other hand, low frequency oscillation of IHR was reduced or abolished by exposure to elevated temperature and was augmented or produced by exposure to lowered temperature even in 0-day-old chicks as the older hatchlings determined previously.