STUDIES ON THE GROWTH AND ATRESIA OF GRAAFIAN FOLLICLES IN THE OVARY OF THE SHEEP

Abstract

Summary. The growth and atresia of individual Graafian follicles in the ovaries of fourteen cycling Suffolk ewes were followed in vivo by marking the large follicle(s) present in the ovaries with Indian ink at three different times during the oestrous cycle. The ovaries containing marked follicles were removed on the 3rd to 9th day of the next cycle and sectioned to determine whether the follicles had ovulated. The results showed that follicles marked before the last day of the cycle regressed and did not ovulate. Only large follicles marked at, or just before, the onset of oestrus, ovulated and developed into corpora lutea. It is suggested that there are at least three phases of follicular growth and atresia during any one oestrous cycle which appear to be independent of circulating progesterone levels. Examination of sections of ovaries from a number of anoestrous and pregnant ewes gave no indication of a similar cyclic pattern of follicular growth and atresia.