Acclimation to hypothermic incubation in developing chicken embryos(Gallus domesticus)

Abstract

SUMMARYHypothermic incubation reduces the ability of the late-stage chicken embryo to mount endothermic heat production. This study investigates whether blood O2 transport is similarly limited by cooler incubation temperatures. Two populations of chicken embryos were incubated at 38°C and 35°C. At Hamilton–Hamburger (HH) developmental stage 41–42, hypothermic incubation had no significant effect on hematocrit(∼26%) or [Hb] (7 g%). However, in the final stages of incubation (stage 43–44), hypothermic incubation reduced hematocrit from ∼31% at 38°C to ∼27.5% at 35°C. Hypothermic incubation similarly caused a reduced [Hb] from 8.5 g% (38°C) to 6.25 g% (35°C), indicating a reduction in blood O2-carrying capacity in embryos. Incubation temperature had a strong effect on blood–O2 affinity in late development (stage 43–44), with P50 at 38°C falling significantly from ∼6 kPa in 38°C embyros to ∼4 kPa in 35°C embryos. PO2 values in chorioallantoic arterial blood at HH 41–42 were 4.3 kPa at pH 7.46 (38°C) and 3.4 kPa at pH 7.39 (35°C). In chorioallantoic venous blood these values were 9.1 kPa at pH 7.34 (38°C) and 8.1 kPa at pH 7.42 (35°C). With further development to HH 43–44, chorioallantoic arterial blood oxygenation fell to 2.4 kPa at pH 7.54 (38°C) and 2.8 kPa at pH 7.52 (35°C). Similarly, PO2 in chorioallantoic venous blood fell slightly to 7.7 kPa at pH 7.42 (38°C) and 7.4 kPa at pH 7.48 (35°C). Collectively, these data reveal that beyond HH 41–42, 35°C embryos experience retarded hematological development, and the findings that support the observed delayed metabolic response to acute temperature changes.