Development of heart rate rhythmicity in Muscovy duck embryos

The heart rate (HR) of Muscovy duck embryos (Cairina moschata f. domestica) was continuously recorded from as early as the 21st day of incubation (D21 ) until hatching (D34/35). The aim of the study was to investigate the infl uence of phonoperiods consisting of different acoustic stimuli on the cours e of HR and the development of HR periodicities during this period. Incubat ion was carried out at a constant temperature and in constant darkness. Unt il D25 HR was dominated by decelerative fluctuations only, indicating a mai n input from the parasympathetic system on the heart. Later sympathetic inf luences increased progressively. HR periodicity was investigated by means o f chi(2)-periodogram and East Fourier transformation. Between D26 and D30 s tatistically significant and stable HR periodicities developed gradually. T hey had periods in the range from 5 to 38 h. Ultra-, circa- and infradian r hythms (< 20, 24 +/- 4 and > 28 h, respectively) occurred in parallel in so me cases in the same embryo. The for the HR course important periods were d issimilar between individual embryos and had different intensities. There w as no indication that acoustic stimulation (phonoperiods) had any effect on the development of HR periodicities. (C) 1999 Elsevier Science Inc. All ri ghts reserved.