Acclimation to hypothermic incubation in developing chicken embryos (Gallus domesticus) -: II.: Hematology and blood O2 transport

Hypothermic incubation reduces the ability of the late-stage chicken embryo to mount endothermic heat production. This study investigates whether blood 02 transport is similarly limited by cooler incubation temperatures. Two populations of chicken embryos were incubated at 38degreesC and 35degreesC. At Hamilton-Hamburger (HH) developmental stage 41-42, hypothermic incubation had no significant effect on hematocrit (similar to 26%) or [Hb] (7 g%). However, in the final stages of incubation (stage 43-44), hypothermic incubation reduced hematocrit from similar to31 % at 38degreesC to similar to27.5 % at 35degreesC. Hypothermic incubation similarly caused a reduced [Hb] from 8.5 g% (38degreesC) to 6.25 g% (35degreesC), indicating a reduction in blood O-2 carrying capacity in embryos. Incubation temperature had a strong effect on blood-O-2 affinity in late development (stage 43-44), with P-50 at 38degreesC falling significantly from similar to6 kPa in 38degreesC embyros to similar to4 kPa in 35degreesC embryos. Po-2 values in chorioallantoic arterial blood at HH 41-42 were 4.3 kPa at pH 7.46 (38degreesC) and 3.4 kPa at pH 7.39 (35degreesC). In chorioallantoic venous blood these values were 9.1 kPa at pH 7.34 (38degreesC) and 8.1 kPa at pH 7.42 (35degreesC). With further development to HH 43-44, chorioallantoic arterial blood oxygenation fell to 2.4 kPa at pH 7.54 (38degreesC) and 2.8 kPa at pH 7.52 (35degreesC). Similarly, Po-2 in chorioallantoic venous blood fell slightly to 7.7 kPa at pH 7.42 (38degreesC) and 7.4 kPa at pH 7.48 (35degreesC). Collectively, these data reveal that beyond HH 41-42, 35degreesC embryos experience retarded hematological development, and the findings that support the observed delayed metabolic response to acute temperature changes.