The Role of the foetal adrenal glands in the mechanism of initiation of parturition in the ewe

Abstract

Pregnancy in the sheep, as in other mammals, has a genetically-determined species-specific duration. It ends with the onset of parturition and the birth of a lamb. The specificity of pregnancy duration must lie in the mechanism by which parturition is initiated – for the length of pregnancy is fixed by the time of its termination. The work of this thesis is an attempt to elucidate some of the factors responsible for ensuring that at the appropriate time the uterus of the pregnant sheep expels its contents. From a review of existing publications it is obvious that the factors influencing gestation length in sheep are poorly understood and that the mechanism of initiation of parturition is unknown. It is fruitless to try to apply knowledge gained in other species to the solution of the problem; among the multitude of hypotheses, none has proved acceptable as a complete description of the events which culminate in parturition in a particular species let alone as a basis secure enough to permit extrapolation to sheep.