Timing of maturation and fertilization of the sheep egg

Abstract

Abstract Eggs of sheep were recovered at known intervals before or after controlled ovulation. They were examined for cytoplasmic and nuclear changes. The vesicular nucleus in the follicular egg persists to 15 hours before ovulation when the chromatin becomes more compact and dense. The first metaphase lasts from 13 hours before ovulation to shortly before ovulation. The formation of the first polar body occurs from four hours before ovulation to ovulation. Normally sheep eggs have formed the first polar body by the time of ovulation and are in the seocond metaphase. Cumulus cells and corona cells are present on the egg at ovulation and for a few hours afterwards. Sperm penetration does not begin ordinarily until at least three hours after ovulation. The male pronucleus forms from 3 to 9 hours after ovulation at about the same time as the female pronucleus. Pronuclei fusion occurs 11 to 22 hours after ovulation. The first mitotic division takes place usually 19 to 24 hours after ovulation although 2‐called eggs were seen at earlier times.