RESPONSES OF DEVELOPING CHICKEN EMBRYOS TO ACUTE CHANGES IN AMBIENT TEMPERATURE: NONINVASIVE STUDY OF HEART RATE

ABSTRACT

Responses of embryonic heart rate to acute changes in ambient temperature were determined in order to elucidate tolerance limits of developing chicken embryos to decreased and increased ambient temperature. The heart rate was measured noninvasively by ballistocardiography, or invasively by electrocardiography, which gave similar results to noninvasive determination. Tolerance to lower temperature was estimated by measuring (1) time of cardiac arrest in 10-day-old embryos exposed to 28, 18, and 8 °C environments and (2) lethal exposure time at 8 °C during development. The embryos survived 8 °C exposure without heartbeat for prolonged periods. The younger the embryo, the longer its tolerance to cardiac arrest at 8 °C. Tolerance to increased temperature was estimated first by determining the lethal ambient temperature for 5 h exposure. Then, the lethal internal egg temperature at 48 °C was determined. The embryos could withstand the increased temperature until their internal egg temperature reached 46–47 °C, regardless of developmental stage. The lethal ambient temperature and tolerance time (i.e., lethal exposure time) may depend upon the time which the egg temperature takes to reach a lethal critical value of 46–47 °C.