Species and fetal gender effects on the endocrinology of pregnancy in elephants

A survey of the management and development of captive African elephant (Loxodonta africana) calves: birth to three months of age

“…In each case, we used the mean and standard deviation cited by the other source as the hypothetical population mean and standard deviation. Our sample was significantly different from the data obtained in situ by Moss [1983]: mean gestation period of 656 ± 4 days obtained for African elephants in situ, D = 0.886, P < 0.01, and from the mean gestation period of 657 ± 6 days found for African elephants ex situ by Meyer et al [2004], D = 0.866, P < 0.01.…”

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

“…This signalling from the female, as in the Asian elephant, is probably through pheromone production (Rasmussen & Schulte 1998) which in turn may be influenced by a hormone stimulus, suggested to be oestrogens as in other mammals, which concurrently prepares the fallopian tubes for conception and the uterus for sperm transport and later implantation. The likelihood that these accessory CL remain dormant in terms of steroid production during at least the remainder of the luteal period, and probably also the first 5-6 weeks of pregnancy, is supported by the present findings of a lack of 3bHSD activity in the luteal cells and those of Meyer et al (2004) of continuing basal levels of progestagen in the peripheral blood of female elephants between the two LH peaks of the inter-luteal period and only a moderate rise in plasma progestagen concentrations after the second LH peak which may reasonably be assumed stems from the primary or gestational CL that develops from the mature (2.0-2.2 cm) follicle which has ovulated normally in response to the second LH peak. And then, at the end of the first 5-6 weeks of gestation, and presumably in response to the luteotrophic action of the commencing elPL secretion by the implanting trophoblast , the 'dormant accessory CL' are stimulated into action, their small luteal cells hypertrophy to form the typically large luteal cells of a mature CL and they then begin to secrete the much larger quantities of progestagens that give rise to the marked, secondary increase in serum progestagen concentrations measured by Meyer et al (2004).…”

“…The likelihood that these accessory CL remain dormant in terms of steroid production during at least the remainder of the luteal period, and probably also the first 5-6 weeks of pregnancy, is supported by the present findings of a lack of 3bHSD activity in the luteal cells and those of Meyer et al (2004) of continuing basal levels of progestagen in the peripheral blood of female elephants between the two LH peaks of the inter-luteal period and only a moderate rise in plasma progestagen concentrations after the second LH peak which may reasonably be assumed stems from the primary or gestational CL that develops from the mature (2.0-2.2 cm) follicle which has ovulated normally in response to the second LH peak. And then, at the end of the first 5-6 weeks of gestation, and presumably in response to the luteotrophic action of the commencing elPL secretion by the implanting trophoblast , the 'dormant accessory CL' are stimulated into action, their small luteal cells hypertrophy to form the typically large luteal cells of a mature CL and they then begin to secrete the much larger quantities of progestagens that give rise to the marked, secondary increase in serum progestagen concentrations measured by Meyer et al (2004). All these pieces of the jigsaw begin to fall into place well, but the mechanism which enables the accessory CL to lie doggo and remain inactive until stimulated by elPL, but in the face of the second pituitary LH release of the interluteal period and the maturation, ovulation, luteinisation and commencing progesterone secretion of the primary (fertile) CL, remains a mystery.…”

“…In both genera these secondary luteal structures make their appearance at the end of the first month of gestation (Amoroso et al 1948, Allen et al 2002 and they appear to form both by ovulation and by luteinisation of unruptured follicles (Allen 1975). Their advent causes a marked secondary rise in progesterone/progestagen concentrations in maternal blood (Allen 1975, Meyer et al 2004. In the pregnant mare, the accessory CLs develop equally on both maternal ovaries as a result of the LH-like biological activity of equine chorionic gonadotrophin (eCG) causing ovulation/luteinisation of mature Graafian follicles stimulated to grow by 10-12 day waves of pituitary FSH released throughout the physiological breeding season in both cycling and pregnant animals (Evans & Irvine 1975, Urwin & Allen 1982.…”

“…These accessory luteal structures, seen clearly by serial transrectal ultrasonographic examinations of the maternal ovaries (Lueders et al 2011), form predominantly, but not exclusively, on the ovary ipsilateral to the uterine horn that will contain the conceptus (Allen et al 2002), and they apparently remain dormant (and non-secretory) during the remainder of the inter-luteal phase, the release of the second ovulation-inducing LH peak (Kapustin et al 1996, Brown et al 1999) and early gestation. They then enlarge greatly to reach diameters of 10-38 mm (Hodges 1998, Lueders et al 2011) and begin to secrete appreciable quantities of 5a-dihydroprogesterone (5aDHP) and other 5a-pregnanes (Hodges et al 1994(Hodges et al , 1997, as evidenced by the sharp increase in maternal serum progestagen concentrations at this time (Meyer et al 2004). Whereas eCG secreted by the foetal endometrial cups (Allen & Moor 1972) is the stimulus for secondary luteal development in the pregnant mare (Allen 1975, Terqui & Palmer 1979, it now seems very likely that placental lactogen (elPL) secreted by the trophoblast from around the time of implantation and commencing development of the zonary endotheliochorial placenta is the essential luteotrophic stimulus in the pregnant elephant .…”