Growth and development of the ovary and small follicle pool from mid fetal life to pre-puberty in the African elephant (Loxodonta africana)

The changing morphology of the ovary is described as the presumptive cortex and medulla components of the fetal ovary settled into their adult form. Interstitial tissue dominated the ovary in late fetal life and these cells stained strongly for 3β–hydroxysteroid dehydrogenase. This staining continued postnatally through to 4.5？years of age suggesting continued secretion of progestagens by the ovary during this period. The considerable growth of antral follicles peaked at 28% of ovarian volume at around 16.7？months of fetal age. The numbers of small follicles (primordial, early primary and true primary), counted in the cortex using stereological protocols, revealed fewer small follicles in the ovaries of animals aged 0 to 4.5？years of age than during either late fetal life or prepubertal life.The small follicle populations of the late-fetal and prepubertal ovaries of the African elephant were described along with the changing morphology of these organs. The changes noted represent a series of events that have been recorded only in the elephant and the giraffe species to date. The expansion of the interstitial tissue of the fetal ovary and its continued presence in early post natal life may well contribute to the control of follicle development in these early years. Further research is required to determine the reasons behind the variation of numbers of small follicles in the ovaries of prepubertal calves.The number of follicles in the ovarian reserve of mammals is established during fetal life or early in neonatal life [1]. From this reserve a number of follicles are recruited each day, the majority of which become atretic while a very few develop to the point of ovulation in each oestrous cycle [2]. The biological norm is therefore to show a steady loss of small follicles throughout life with the resulting depletion of the follicle reserve [3]. This dogma has been challenged in recent years and the debate on neo-oogenesis and the existence of post-natal oogonial ste