Acclimation to hypothermic incubation in developing chicken embryos (Gallus domesticus) -: I.: Developmental effects and chronic and acute metabolic adjustments

Chronic exposure to a low incubation temperature clearly slows the development of poikilothemic chicken embryos (or any other poikilotherms), but little is known about the more subtle developmental effects of temperature, especially on physiological regulatory systems. Consequently, two populations of chicken embryos were incubated at 38degreesC and 35degreesC. When compared at the same development stage, incubation temperature had no significant impact on embryonic survival or growth. Moreover, the relative timing of major developmental landmarks (e.g. internal pipping), expressed as a percentage of development, was unaffected by temperature. The ability to maintain the rate of oxygen consumption (Vo(2)) during an acute drop in ambient temperature (T.) improved from Hamburger-Hamilton (HH) stages 39-40 to 43-44 in the 38degreesC but not the 35degreesC populations. Late stage (HH43-44) embryos incubated at 38degreesC could maintain Vo(2), (approximately 27-33 mul g(-1) min(-1)) during an acute drop in T-a to approximately 30degreesC. However, at the same stage 35degreesC embryos acutely measured at 38degreesC were unable to similarly maintain their Vo(2), which fell as soon as T-a reached 36degreesC. Thus, while hypothermic incubation does not affect gross development (other than would be predicted from a simple effect of Q(10)), there is a significant delay in the relative timing of the onset of thermoregulatory ability induced by hypothermic incubation.