The progression of small-follicle reserves in the ovaries of wild African elephants (Loxodonta africana) from puberty to reproductive senescence.

This study aimed to determine whether the follicle reserve in the ovary of the African elephant declines progressively after puberty and whether its depletion constrains the fertility of older females. Elephant ovaries were fixed in 4% neutral buffered formalin and small-follicle counts made using stereological protocols. Excepting a slight rise in small-follicle numbers between 16 and 25 years of age, there was a trend for follicle numbers to fall from puberty to 70 years. Reproductive status did not impact significantly on small-follicle numbers (P=0.31). The number of early primary follicles, initially higher in number than true primary follicles, fell from post-puberty to nil at 45 years of age. Six of the seven oldest animals in the study showed signs of recent ovarian activity in the form of antral follicles, corpora lutea or large corpora nigra. The four oldest elephants (mean age 69 years) had a median small-follicle count of 11,113. In summary, it appears that the elephant ovary is capable of supplying oocytes for ovulation right up to the time of death at the age of maximum life expectancy, although the follicle reserve becomes depleted in some older elephants.

Development of the germinal ridge and ovary in the African elephant (Loxodonta africana).

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.

Luteal maintenance of pregnancy in the African elephant (Loxodonta africana).

The ovaries of eight African elephant foetuses and their mothers between 2 and 22 months of gestation, and those of two cycling and two lactating elephants, were examined grossly, histologically and immunocytochemically, with emphasis on the development and regression of accessory corpora lutea (CL) of pregnancy and the steroidogenic capacities of the accessory CL and the foetal ovaries. The results supported recent findings that the accessory CL form as a result of luteinisation, with and without ovulation, of medium-sized follicles during the 3-week inter-luteal period of the oestrous cycle. They enlarge significantly and become steroidogenically active around 5 weeks of gestation, probably in response to the placental lactogen which is secreted by the implanting trophoblast of the conceptus. The large luteal cells stained strongly for 3ß hydroxysteroid dehydrogenase (3ßHSD) activity throughout the 22-month gestation period although they showed vacuolation and other degenerative changes in the final months of gestation coincident with hypertrophy and hyperplasia of 3ßHSD-positive interstitial cells in the foetal gonads. It is proposed that the progestagens secreted by the enlarged gonads of the elephant foetus may function both to assist the maternal ovaries in supporting the pregnancy state and to induce torpor and intrauterine immobility of the rapidly growing foetus.

Placentation in the African elephant (Loxodonta africana). V: the trophoblast secretes placental lactogen.

OBJECTIVES: To determine if elephant placenta secretes a lactogenic hormone which may function as the principal luteotrophin to maintain ovarian luteal function throughout gestation. STUDY DESIGN AND MAIN OUTCOME MEASURES: To label biopsies of endometrium and placenta recovered from African elephant culled professionally throughout gestation with an anti-human prolactin polyclonal antibody in a conventional immunocytochemical staining technique. RESULTS: All trophoblast cells covering the placental villi and forming 'plugs' in the apical endometrial glands stained strongly and precisely with the anti-human prolactin antiserum throughout gestation. CONCLUSIONS: Elephant trophoblast secretes a placental lactogen (elPL) which may stimulate both the development and secretory function of the large accessory corpora lutea of elephant pregnancy and provide the mitogenic stimulus for placental differentiation and development.