Efficiency of Thermoregulatory Control Elements in Precocial Poultry Embryos

Toexplainallaspectsof theefficiencyof thethermoregulatorysysteminpoultryembryos,theactivityandthedynamicsofdifferent control elements have to be investigated systematically during the prenatal period.The relevant methodology and results, citedinthispaperaremainly fromourowngroupbutarecomparedwithrelatedexperimentsdescribedinthescientificliterature. They may be summarised: Thermoregulatory behaviour is developed early in poultry embryos. Temperature of allantoic fluid (Taf) represents the internal body temperature in the last third of incubation because Taf and Tc are much the same at normal (37.5C) and low incubation temperatures (34.5C) after internal pipping. Fowl embryos show endothermic reactions from day14 and Muscovy duck embryos from day 22. In precocial avian embryos, body core temperature increases in accordance with heat production. In contrast to heat production the efficiency of heat loss is high in precocial avian embryos. Development of physiologicalcontrol systems starts withnon-co-ordinatedandproximate (immediate) non-adaptive reactions. In summary, endothermic reactions occur very early during embryonic development but their efficiency is limited. Due to the van’t Hoff rule, low temperatures decrease the net heat production but the trajectories of endothermy are stimulated and related epigenetic adaptation mechanisms are activated. Using behavioural mechanisms the embryo is protected against super-cooling during the natural incubation process. The heat loss mechanisms are most efficient against heat stress, which may occur for only very short time during incubation, protect the embryo against disturbances caused by hyperthermia.