Electrolyte and Water Balance of the Early Avian Embryo: Effects of Egg Turning

Formation of sub-embryonic fluid (SEF) is a key aspect of the physiology of the early avian embryo.Here we review the process of SEF formation and the factors which influence its composition and the rate of SEF production and depletion in the Japanese quail and domestic fowl.There is particular emphasis on the role of turning of the egg during incubation and we briefly consider the broader role of egg turning during avian incubation. The bulk of the review deals with the growth of the area vasculosa of the yolk sac membrane, the cellular processes of SEF formation, and the water and electrolyte physiology of the avian embryo during the first half of incubation.We conclude with a brief discussion of the areas for future investigation.