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Early embryo development in the elephant assessed by serial

ultrasound examinations

B. Drews a,*, R. Hermes a, F. Göritz a, C. Gray b, J. Kurz c, I. Lueders a, T.B. Hildebrandt a

a Leibniz Institute for Zoo- and Wildlife Research, PF 601 103, 10252 Berlin, Germany b African Lion Safari, Cambridge, ON, Canada N1R 5S2

c Jürgen Kurz Römerstr. 12, 4800 Attnang-Puchheim, Austria

Received 17 September 2007; received in revised form 21 December 2007; accepted 29 January 2008

Abstract

The elephant has an extraordinary long pregnancy, lasting 21 months. However, knowledge on embryo development is limited.

To date, only single morphological observations of elephant embryo development associated with placentation are available, all

lacking correlation to gestational age. The present study describes morphological characteristics of early embryo development in

the elephant with exact biometric staging. Six pregnancies in five Asian and one African elephants with known conception dates

were followed by 2D and 3D ultrasound, covering the embryonic period from ovulation to day 116 post-ovulation. The embryonic

vesicle was earliest observed was on day 50 p.o. The proper embryo was not detected until day 62 p.o. Embryonic heartbeat was first

observed on day 71 p.o. The allantois, which became visible as a single sacculation on day 71 p.o. was subdivided in four

compartments on day 76 p.o. By day 95 p.o., head, rump, front and hind legs were clearly distinguished. Between days 95 and 103

p.o. the choriovitelline placenta was replaced by the chorioallantoic placenta. A physiological midgut herniation was transiently

present between days 95 and 116 p.o. On the basis of the late appearance of the embryonic vesicle, delayed implantation in the

elephant is discussed. The study provides a coherent description of elephant embryonic development, formation of the

extraembryonic organs and their role in placenta formation, all of which are of interest for both comparative evolutionary studies

and the improvement of assisted reproduction techniques.

# 2008 Elsevier Inc. All rights reserved.

Keywords: Elephant; Reproduction; Embryogenesis; Ultrasound; Extraembryonic organs

1. Introduction

The situation of the African (Loxodonta africana) and

Asian elephant (Elephas maximus) in their respective

native countries is quite different. In Asia, the ever-

growing human population repels the wild-elephant

population to restricted areas. To ensure their survival,

* Corresponding author at: Leibniz Institute for Zoo- and Wildlife

Research, Alfred-Kowalke-Str. 17, 10315 Berlin, Germany.

Tel.: +49 30 5168246; fax: +49 305126104.

E-mail address: drews@izw-berlin.de (B. Drews).

0093-691X/$ – see front matter # 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2008.01.026

wild-elephant herds are thus forced to raid crops, causing

severe conflict with man. Furthermore, natural habitats

are more and more fragmented, separating subpopula-

tions and impeding genetic exchange [1].

From historical reports it is known that the African

elephant once inhabited the whole continent [2].

Extensive ivory trade dating back as far as in Roman

times [3], expanding human settlements [4] and civil

wars [5] are associated with a decline of the African

elephant population. Elephants have long vanished from

North Africa and populations are greatly diminished in

West, Central and East Africa [6].

mailto:drews@izw-berlin.de
http://dx.doi.org/10.1016/j.theriogenology.2008.01.026

B. Drews et al. / Theriogenology 69 (2008) 1120–1128 1121

In Southern Africa, where the elephant population

had almost gone extinct due to ivory poaching in the

19th century, numerous National parks have been

founded to save the species. Here, elephant numbers in

protected areas continuously build up and lead to local

overpopulations. In the Kruger National Park, an

estimated population of 10 individuals in 1908

augmented to approximately 6500 elephants 60 years

later [7]. According to the South African National

Parks Board, this number overstrained the natural

capacities of the park. In 1965 it was decided to limit

the elephant population to 7000 animals. In the

following 18 years, about 16,200 elephants were

culled. Due to political and public pressure, the culling

policy was abandoned in 1994. Since then, elephant

numbers in the park increase by 7% per annum and

culling is reconsidered [8].

In captivity, breeding success is still insufficient to

come by Wiese reported that without imports from the

wild or dramatically improved fecundity, the captive

Asian elephant population in North America will

decline to 10 individuals in 50 years [9]. The prospect

for the captive North American African elephant

population, with a decline of 2% per year, is almost

equally alarming [10]. Reasons for poor reproduction in

captivity are numerous. Proven breeder bulls are rare

and the majority of captive females that were once

imported from the wild are now post reproductive age.

To improve captive breeding, ultrasound guided

artificial insemination was developed [11–13].

In light of the elephant situation in the wild and in

captivity it is obvious that more knowledge about its

reproductive biology is needed. Our understanding of its

embryogenesis in particular will enhance our abilities to

manage in situ and ex situ populations appropriately.

Foetal specimens collected during culls provided for

our knowledge on elephant prenatal development [14]

and placentation [15–18]. However, the age of the

specimens described was not known and the develop-

ment of the embryo could not be correlated to the

Table 1

Pregnant elephants examined by 2D and 3D ultrasound

Scanned elephant Species Studbook # Institution

Elephant 1 Laa 143 Indianapolis Zoo, In

Elephant 2 Emb 356 African Lion Safari,

Elephant 3 Em 264 African Lion Safari,

Elephant 4 Em 347 African Lion Safari,

Elephant 5 Em 8403 Whipsnade Wild An

Elephant 6 Em 424 African Lion Safari,

a African elephant (Loxodonta africana). b Asian elephant (Elephas maximus).

development of its extraembryonic organs and placenta

formation. Since gestational age was not known,

specimens were classified according to their body mass

[19,20]. Growth curves derived from newly published

data showed a systematic error in previously published

growths graphs of up to 60 days [21].

Transrectal ultrasound was already employed in field

contraception studies conducted between 1996 and

1998 in the Kruger National Park in South Africa [22].

Using ultrasound, the reproductive status of the

elephant was determined prior subcutaneous implanta-

tion of contraceptive hormones to avoid hormone

treatment of pregnant animals. However, 3 of 57

animals that were diagnosed as non-pregnant and

treated with contraceptives turned out to be pregnant

when a second ultrasound exam was performed 1 year

later. These preliminary findings suggested a delayed

implantation in the elephant and prompted us to conduct

further study of elephant embryo development pre-

sented here. This study aimed to describe the early

embryonic development in elephants as seen by

transrectal 2D and 3D ultrasound in correlation with

gestational age with a special focus on depicting the

topographic relationship of the extraembryonic organs

and their function in placental formation.

2. Materials and methods

2.1. Elephants

Five Asian elephants (E. maximus) and one African

elephant (L. africana) were examined (Table 1). All

elephants were kept in free contact management setting.

Gestational age in the six females was known from

artificial insemination (n = 1) or observed mating

(n = 5) and corresponded with LH and progesterone

measurements [23,24]. In addition to hormonal data, the

rupture of the leading follicle was monitored by

ultrasound. The day of ovulation was defined as day

0 of gestation.

No. of exams Gestational age (days p.o.)

dianapolis, USA 4 37, 44, 58, 62

Cambridge, CA 12 67–112

Cambridge, CA 17 12–115

Cambridge, CA 28 38–116

imal Park, GB 3 74, 89, 116

Cambridge, CA 46 52–116

Hanifa Ghaznawi
Hanifa Ghaznawi
Hanifa Ghaznawi
Hanifa Ghaznawi
Hanifa Ghaznawi
Hanifa Ghaznawi
Background
Hanifa Ghaznawi
hypothese
Hanifa Ghaznawi

B. Drews et al. / Theriogenology 69 (2008) 1120–11281122

2.2. Ultrasound examination

Transrectal ultrasound examinations were performed

as described by Hildebrandt et al. [25]. The number of

ultrasound examinations during the embryonic period

(days 0–116 post-ovulation, p.o.) ranged from 3 to 37

per animal (Table 1). The ultrasound systems used in

this study included the stationary Voluson 530 and

Voluson 730 and the portable Voluson ‘‘i’’ (GE

Healthcare, Austria).

Using 3D ultrasound, the structure of interest was

first located with conventional 2D ultrasound before

switching to volume mode. While the hand of the

examiner did not move, the transducer was automati-

cally pivoted over the predefined area by a probe

internal motor. The volume was acquired by scanning a

set of consecutive 2D planes and continuously storing

the images. The pixel were interpolated into voxel.

Seconds after acquisition, the scanned region was

displayed on the screen. It was then checked if the

volume contained the structure of interest and if

necessary, the scan was repeated.

All ultrasound examinations were recorded on

miniDV tapes (GV 100P, Sony Inc., Japan) for

retrospective analysis. 3D scans were stored on

magneto-optical-discs or CD. Each ultrasound exam-

ination took between 30 and 90 min.

2.3. Retrospective analysis

For retrospective analysis, every ultrasound record-

ing was carefully viewed with a video recorder

connected to a monitor. Video sequences were

digitalized (Adobe Premiere Pro 1.5, Adobe1 Systems

Inc., USA) and characteristic sonograms were gener-

ated and stored as jpeg-files. For the measurement of

biometric parameters (analySIS1 Soft Imaging System

GmbH, Germany), the optimal plane showing the

structure in full extent was selected. For the evaluation

of the 3D scans, the volume data could be displayed in

Fig. 1. bar = 10 mm (A) Sonogram of free fluid (arrows) within the lumen

vesicle (Ev) at day 52 p.o. (C) Sonogram of the embryonic vesicle with the em

day 63 p.o.

three different modes: multiplanar mode, render mode

and inverse render mode (4DView, GE Healthcare,

Austria). In multiplanar mode, the object of interest is

displayed simultaneously in three perpendicular planes

(sagittal, transverse and frontal). In this way the

structure to be measured was depicted in its optimal

plane and measurements were taken without prior

calibration. The free rotation of the object and the

choice of different section planes permitted the

topographic analysis of the scanned volume. In render

mode the embryo was depicted in a 3D view, giving an

impression of its surface structure. In contrast, the

algorithms of the inverse render mode visualize those

parts of the data set which are anechoic, such as fluid

filled cavities. Thus the size, location and changes in

formation of the yolk sac, the amnion and the allantois

could be visualized.

3. Results

3.1. Embryonic vesicle

In weeks 1–4 p.o., the endometrium appeared

hyperechogenic and was barely distinguishable from

the myometrium. In week 5 p.o., the endometrium

increased in thickness and appeared hypochechogenic

compared to the myometrium. Between days 36 and

45 p.o., free fluid within the uterus was observed. On

day 46 p.o., the fluid accumulation became more

distinct (Fig. 1A). A definitive embryonic vesicle

could not yet be visualized. An embryonic vesicle,

clearly defined by two hyperechoic lines, was

depicted for the first time on day 50 p.o. (Fig. 1B).

It was found in the lower section of the uterine horn

(pseudouterine body), ipsilateral to the ovary where

ovulation had occurred. The diameter of the round-

shaped vesicle was 8 mm. The endometrium sur-

rounding the embryonic vesicle appeared darker than

the rest of the endometrium, indicative for the

decidual reaction of the implantation site.

of the uterine horn (dashed arrows). (B) Sonogram of the embryonic

bryonic disc (Ed) at day 59 p.o. (D) Sonogram of the embryo proper at

Hanifa Ghaznawi

B. Drews et al. / Theriogenology 69 (2008) 1120–1128 1123

3.2. Choriovitelline placenta and formation of the

embryo

A faint hyperechoic dot close to the endometrium on

day 59 p.o. indicated evidence of embryonic tissue

(Fig. 1C). The still round shaped embryonic vesicle had

increased to 30 � 0.2 mm. A definite embryonic structure of 5 mm became visible on day 62 p.o. when

the embryonic vesicle was 35 mm in diameter (Fig. 1D).

Embryonic heartbeat was detected as flickering motion

on day 71 p.o. The embryonic heart was also identified

by colour Doppler. On day 76 p.o., a thin membrane

divided the embryonic vesicle into two compartments of

unequal size. The larger compartment, ventral to the

now 7-mm embryo, was identified as yolk sac and the

smaller compartment dorsal to the embryo as not yet

divided allantois. For identification of the different

cavities the structures were traced back from later stages

where they were unambiguous. The yolk sac was large

and filled the greatest part of the embryonic vesicle. At

the abembryonic pole it was flattened and in full contact

with the underlying endometrium, providing evidence

for a functional choriovitelline placenta. The amniotic

cavity could not be depicted at that stage.

3.3. Chorioallantoic placenta

On day 73 p.o., a subdivision of the allantois in four

compartments became visible. In close proximity to the

embryo (15 mm), the endometrium protruded into the

chorioallantoic cavity. This part of the endometrium

appeared slightly hyperechoic and denoted the begin-

ning development of the chorioallantoic placenta.

With the progressing pregnancy, the embryo showed

a dorsoconvex flexure and head and rump could be

distinguished from day 83 p.o. onwards. The allantoic

compartments increased in size, embracing the yolk sac

from its lateral sides. The yolk sac was oval in shape and

still formed a choriovitelline placenta at the abem-

bryonic pole. At the transition of the allantoic

compartments to the choriovitelline placenta sac, the

adjacent endometrium was slightly hyperechoic,

demonstrating endometrial activation. A small hypoe-

choic cavity around the embryo was identified as

amniotic fluid limited by a fine allantoamniotic

membrane. On day 85 p.o., the architecture of the

allantoic compartments was clearly depicted (Fig. 2A)

and individual differences in the topography became

evident. In 2D mode, the allantochorionic placenta was

seen as protrusion into the embryonic vesicle. In inverse

render mode, the indentation of the allantoic sacculation

alluded to the allantochorionic placenta (Fig. 2B). The

embryo itself could not be outlined in inverse render

mode. Its position was indicated by the oval shaped

impression of the yolk sac (Fig. 2B).

Beginning on day 95 p.o., fore and hind limb buds of

the embryo were observed and the triangular nose

clearly characterised the embryo as an elephant

(Fig. 2C). A widening of the umbilical cord was

identified as physiological midgut herniation. The

allantoic compartments had increased in size and

reached the abembryonic pole, almost separating the

yolk sac from the endometrium (Fig. 2C and D). Further

development of the allantochorionic placenta resulted

in the formation of a placental band, which was not yet

completed. The form and volumes of the allantoic

compartments and the yolk sac greatly varied between

the different elephants as well as between the different

examination days of the same elephant. This phenom-

enon can be explained by the fact that the chorioal-

lantoic membrane, which is not involved in

placentation, is not attached to the endometrium. The

filling of the guts, the positioning of the pregnant

elephant during the exam and the position of the uterus

therefore influence the topography of the allantoic

compartments. The double membranes which are

formed by the adjacent allantoic sacculations were

also free, so that the embryo itself was not bound to a

constant position in relation to the placenta, either. It

was found in parallel as well as in perpendicular

position to the placental band. Between days 95 and 102

p.o., front and hind limb buds of the embryo had grown

to proper feet and movements of the latter were

observed. The nose had elongated in a short trunk and

the ears appeared as roundish structures lateral of the

head. The ring formation of the chorioallantoic placenta

was completed between days 97 and 103 p.o. However,

in two females, the principle placental ring formation

remained interrupted in one and two sections, respec-

tively. These sonographic findings were confirmed in

one elephant by the examination of the afterbirth. The

yolk sac became pedunculated beginning on day 97 p.o.

Due to its long stalk, it could be observed ventral or

dorsal to the embryo. Beginning on day 100 p.o., the

different embryonic compartments were better distin-

guished as their fluid quality changed: the quality of the

allantoic fluid became more echo dense in contrast to

the yolk sac fluid which remained hypoechoic and clear.

With advancing gestation, the embryo increased in

size and filled the greater part of the chorioallantoic

cavity, so that it was frequently found in perpendicular

position to the placental band from day 110 p.o.

onwards. With the elongated and slightly curved trunk,

the big ears and the feet with their characteristic flat

B. Drews et al. / Theriogenology 69 (2008) 1120–11281124

Fig. 2. bar = 10 mm (A) Sonogram of elephant conceptus at day 83 p.o. with embryo (Em), chorioallantoic placenta (Pl), allantoic sacculations (Al)

and Yolk sac (Ys). (B) 3D sonograms of the same conceptus at day 83 p.o. in inverse render mode depicting the topography of allantoic sacculations

(Al) and yolk sac (Ys). The position of the embryo can be deduced from the impression of the yolk sac. (C) Sonogram of elephant conceptus at day 95

p.o. The allantoic sacculations (Al) have enlarged and begin to displace the yolk sac (Ys) from the endometrium. The trunk (Tr) and forelimb buds

(Fl) of the embryo are recognizable. The amnion is a fine membrane surrounding the embryo. The allantochorionic placenta (Pl) protrudes into the

allantochorionic cavity. (D) 3D sonogram of elephant conceptus at day 95 p.o. in inverse render mode, illustrating the volumes of allantois (Al) and

yolk sac (Ys). The allantoic sacculations embrace the embryo from lateral and dorsal. (E) 3D sonogram in render mode of elephant conceptus at day

116 p.o. The embryo has developed into a foetus, which displays the typical elephant shaped trunk (Tr), ear (Ea), front (Fl) and hind legs (Hl). On its

ventral side, the paired allantoic vessels (Av) that travel to the placenta (Pl) can be seen. (F) 3D sonogram in inverse render mode of the same

conceptus at day 116 p.o. The ring shaped impression of the allantois (Al) marks the fully established chorioallantoic placenta. The pedunculated

yolk (Ys) sac has greatly diminished in size. (G) Sonogram of an embryo at day 73 p.o. (H) Corresponding drawing of an early conceptus according

to Perry depicting free uterine lumen (Ul), the different germ layers and extraembryonic organs (Am—amnion, Al—allantois, Ys—yolk sac).

Mesoderm is indicated as red-hatched line, trophoblast as blue line and the surrounding endometrial layer as black line.

B. Drews et al. / Theriogenology 69 (2008) 1120–1128 1125

sole, the outer shape of the embryo showed a great

alikeness to its adult counterpart (Fig. 2E), indicating

the end of the embryonic period. Close to the abdomen,

the subdivision of the umbilical vessels became visible

(Fig. 2E). The yolk sac was still present, but had shrunk

considerably until day 116 p.o. (Fig. 2F).

4. Discussion

In literature, description of early embryonic devel-

opment in the elephant in association with the formation

of the extraembryonic organs was hampered by lack of

adequate age determination and scarce availability of

early specimens. Since the age of the specimens was not

known to the authors, a direct comparison with the

images obtained by ultrasound was not possible.

However, the 3D ultrasound technique provided the

free selection of plane within the 3D volume data sets.

With this method it was possible to depict ultrasound

sections which corresponded to the histological sections

published in literature [16]. The comparison of the

conceptus of known age as seen by ultrasound allowed

the reliable age determination of the previously

published embryo data [16–18].

4.1. Early blastocyst

Embryonic development in general begins with the

fertilization of the oocyte within the oviduct. Fertiliza-

tion triggers cleavage of the fertilized oocyte to the

morula and eventually to the blastocyst stage while it

travels down the oviduct to the uterus. Before it attaches

to the uterine wall, the blastocyst moves freely within

the uterine lumen. The time period between ovulation

and implantation differs greatly between species

(human: 20 days [26], dog: 12 days [27], sheep: 16

days [28]). In our study, an embryonic vesicle or

blastocyst with a diameter of 8 mm could first be

detected by ultrasound on day 50 p.o. Perry described a

bilaminar blastocyst in the pre-attachment phase with a

diameter of 10 mm after fixation [16]. Allen and co-

workers rescued two specimens that consisted of a

choriovitelline membrane containing several millilitres

of fluid [17,18]. These specimens were obviously in a

later developmental stage since the trophoblast was

already attached to the endometrium [17,18]. From the

comparison of the ultrasound data with the available

histological data we conclude that the blastocyst

observed by ultrasound was still in an early stage of

implantation. The time period between ovulation and

implantation is therefore extended, suggesting that the

elephant exhibits delayed implantation.

Delayed implantation or diapause is a typical feature

of marsupials [29], enabling the lactating mother to

store an unimplanted blastocyst in an arrested stage of

development in the uterus. If the newborn is removed

from the pouch, the quiescent blastocyst reassumes its

development. Other mammalian species that exhibit

delayed implantation independent from lactation

include bears [30], mustelids [31], and the European

roe deer as the so far only member of the artiodactyls

described [32]. In the European roe deer, the hatched

blastocyst exhibits reduced mitotic activity for 5 months

and only reassumes its normal development shortly

before implantation [33,34]. During implantation,

serum progesterone levels are elevated [35,36]. Inter-

estingly, the period of implantation in the elephant also

coincides with a first rise in serum progesterone in

weeks 6–8 p.o. [37].

4.2. Development of the embryo proper and the

extraembryonic organs

Before the conceptus establishes its placenta, it

forms its extraembryonic organs such as amnion, yolk

sac and allantois. The amniotic membrane directly

envelops the embryo with its fluid representing the

water environment where the life of vertebrates started.

Yolk sac and allantois play an important role in placenta

formation since their mesoderm provides the vascular

supply of the placenta. Whereas the choriovitelline

placenta is the definitive placenta of marsupials, it is

only transiently present in some eutherians and replaced

by the chorioallantoic placenta early in ontogenesis

[38]. A choriovitelline placenta was also described in

the elephant [16–18].

An embryonic disc was first observed by ultrasound

on day 59 p.o., when the blastocyst had a diameter of

30 mm. The respective developmental stage described

by Perry was a blastocyst consisting mainly of a large

primitive yolk sac where mesoderm formation had just

started and an embryonic disc was present [16].

By ultrasound, the embryonic disc formed into a

definite embryonic structure on day 62 p.o. and the yolk

sac was in contact with the surrounding endometrium. A

conceptus described by Perry contained an embryo of

5 mm which was folded off and closely invested in its

amnion [16]. A mesoderm covered yolk sac was

present. Perry assumed that the yolk sac in this

specimen was near its maximum size. The uncomparted

allantois had just reached the chorion at one place and

exocoel was described [16]. By sonography, an allantoic

vesicle was observed on day 71 p.o., when the embryo

had a size of 7 mm. By that time, the flattened yolk sac

Hanifa Ghaznawi

B. Drews et al. / Theriogenology 69 (2008) 1120–11281126

at the abembryonic pole, closely applied to the

underlying endometrium, demonstrated a functional

choriovitelline placenta.

When the sonogram of the embryo on day 71 p.o.

(Fig. 2G) is compared to Perry’s drawing of a 5-mm

embryo (Fig. 2H) the similarity of the two images is

striking. Although the embryo observed by ultrasono-

graphy on day 71 measured already 7 mm, the size

difference can be neglected due to the morphological

alikeness. In the ultrasound image, no free uterine lumen

can be observed. The free uterine lumen described by

Perry suggests that attachment is only superficial and that

the trophoblast was detached during processing.

On day 76 p.o. the allantois became comparted and

the chorioallantoic placenta began to develop. The yolk

sac was still large and in contact with the endometrium.

A subdivision of the allantois was described by Perry in

an embryo of 20 mm [16]. The architecture of the

allantoic compartments could not be reconstructed

owing to fragmentation during fixation. The yolk sac in

this specimen had considerably reduced. Perry’s

embryo of 20 mm in length corresponds to an age of

Fig. 3. Depiction of the embryonic and foetal period of the elephant. The dif

are shown on an explosion of the time axis. The time window for transrectal

depicted by a violet line, the yolk sac by an orange line. The allantoic comp

allantoic compartments are outlined although the typical subdivision in four

by crosshatch.

approximately 83 days [16]. In contrast to the

observation of Perry, our ultrasound data show that

the yolk sac at this stage is prominent and forms a

choriovitelline placenta. The choriovitelline placenta is

replaced by the chorioallantoic placenta between days

95 and 103, when the embryo has formed fore and hind

limbs and the trunk begins to develop. On day 116,

when the embryonic period has reached its end and the

foetus displays its typical elephant shape, the yolk sac is

still visible but considerably diminished in size. The

embryonic development of the elephant as described in

this study is illustrated in Fig. 3

The shift of the allantoic fluid quality from clear to

cloudy around day 100 p.o. indicates the production of

urine by the well developed and functionally active

mesonephros of the elephant [14]. The amniotic cavity

was found to be very small compared to the allantoic

sacculations. From this observation we conclude that

the allantois provides for the greatest part of the foetal

fluids. The rupture of the allantoic sacculations during

the birthing process facilitates easy down gliding of the

foetus through the long-urogenital tract of its mother.

ferent morphological stages of the embryonic period (days 0–116 p.o.)

ultrasonography is from days 0 to 240 p.o. The trophoblast/chorion is

artments are shown as a green line. Owing to the 2D graph, only two

compartments was observed. The chorioallantoic placenta is indicated

B. Drews et al. / Theriogenology 69 (2008) 1120–1128 1127

In conclusion the longitudinal ultrasound monitoring

provides not only exact staging of the embryo but also

contributes to morphological description of early

implantation stages, extraembryonic organs and the

development of the elephant embryo.

Acknowledgements

The authors thank the staff at the African Lion Safari,

CA and at Whipsnade Zoo, GB, for their great elephant

expertise and support. The work at the African Lion

Safari has been funded by a grant of the German

Scientific Exchange Service (DAAD).

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Early embryo development in the elephant assessed by serial ultrasound examinations
Introduction
Materials and methods
Elephants
Ultrasound examination
Retrospective analysis
Results
Embryonic vesicle
Choriovitelline placenta and formation of the embryo
Chorioallantoic placenta
Discussion
Early blastocyst
Development of the embryo proper and the extraembryonic organs
Acknowledgements