Abstract:
The follicular reserve and its ontogeny in the elephant are of interest because elephants have
the longest reproductive life of all land-based mammals. They also have the longest recorded
pregnancy which allows a protracted view of the series of significant events involved in the
development of the embryonic and fetal gonads. The large elephant population of Zimbabwe
provided the opportunity to collect conceptuses from elephants culled for management
reasons and hunted professionally. Five embryos aged 76–96 days and the ovaries of four
fetuses aged 4.8–11.2 months were fixed in 4% buffered formalin and studied by
conventional histological sectioning and a stereological protocol to calculate the follicle
reserve of each fetus. These observations enabled the conclusion that the migration of
primordial germ cells into the indifferent gonad terminates at around 76 days of gestation
while entry of oogonia into meiosis along with first follicle formation starts at around 5
months. Peak numbers of follicles are present by mid-gestation towards the end of the 6
month mitotic-meiotic transition period. It appears that the cortex of the elephant fetal ovary
at mid-gestation (11 months) has already reached a developmental stage exhibited by the
ovaries of many other mammals at full term.
