Wildebeest, Gnu (Connochaetes taurinus; C. gnou)

Order: Artiodactyla

Family: Bovidae

1) General Zoological Data

Two species are recognized: the much more common brindled gnu (also white-bearded or blue gnu) and the smaller white-tailed gnu (black gnu). Connochaetes derives from konnos (Greek = beard) and khaite (flowing hair), while gnou is said to be Hottentot for the antelope (Gotch, 1979). The white-tailed gnu is now very rare and perhaps limited to areas of Namibia, while the blue wildebeest exists in larger regions of South and Southeast Africa and is well-known because of its large migrations. It is also much more common in zoological gardens, the former being very uncommonly seen now. Several subspecies have been described of the blue gnu that are mainly regional color variants. Adults weigh up to 275 kg, neonates weigh around 22 kg. Longevity is over 21 years (Jones, 1993).

Corbet & Robinson (1991) estimated the divergence time of these two species as 1 MYA from mtDNA studies. Arctander et al. (1999) studied mtDNA regions of three alcelaphine species (gnu, topi, hartebeest) and found them to be closely related. Moreover, they provided evidence that they had been much more widely distributed over Africa in the past.

Connochaetes gnou. 

Connochaetes taurinus taurinus. 

Connochaetes taurinus albijubatus. 

2) General Gestational Data

Reproduction of wildebeest is highly seasonal in Africa. The length of gestation is 8-9 months (250-260 days) with single offspring weighing 20-22 kg. Age of first conception is about 28 months (Mentis, 1972). Placentas weigh between 1,500 and 1,800 g. Estes & Estes (1979) reviewed the social organization of wildebeest and make reference to the high neonatal survival among wildebeest calves in the Ngorongoro Park.

3) Implantation

No details are known of early implantations or interaction of blastocyst with endometrium.

4) General Characterization of the Placenta

This is a polycotyledonary placenta; no perceptible difference was found between the two species. Both have about 40 cotyledons, arranged in four rows. The weight of one of my term brindled gnu placentas was 1,575 g (37 x 11 cm). The placenta of a white-tailed gnu weighed 1,870 g. The cotyledons measured up to 10 cm in greatest diameter and were remarkably thin (0.3 cm). Hradecky (1983) published different numbers of cotyledons: in both species there were four rows of cotyledons but the number of cotyledons varied from 58 to 104, with a maximal size 11 x 6 cm. He found, roughly, that one-half of the cotyledons were fewer than 5 cm in diameter. Later, Hradecky (1988) described in more detail the structure of placentomes. He measured the villi as being 8 mm long and indistinct at their tips. They had few branches.

Implanted term placental cotyledon; uterus below.

Implanted term placental cotyledon; uterus below.

5) Details of fetal/maternal barrier

The barrier is epithelio-chorial and there is no infiltration of the uterus by trophoblast. Beneath the chorionic surface of at least one of the two mature placentas there was degeneration of the subchorionic tips of the maternal septa with some hemorrhage. A few of the cylindrical trophoblast beneath the chorion has incorporated yellow pigment. It was iron-staining negative. The villi are covered by a single layer of cuboidal trophoblast with a large number of binucleate cells, investigated in other ruminants by Wooding (1982) as well as by Atkinson et al. (1993). The latter produce glycoproteins and, most likely as in other ungulates, are responsible for the secretion of placental lactogen.

Chorion above with cylindrical trophoblast and red, degenerated debris and blood next to maternal septum.

Villi at left, center and right with arrows pointing to binucleate cells. Two dense maternal septa are also present.

Higher magnification of binucleate cells at arrows.

Implantation site with dense endometrium below and maternal septa spanning up between lighter-staining villi. Here there are no endometrial glands.

Another implantation site with remaining endometrial glands.

Immature placental surface of delivered (detached) placenta with larger villi.

6) Umbilical cord

The umbilical cord contains 4 large blood vessels, an allantoic duct and a number of small blood vessels. Numerous foci of squamous metaplasia are found on the surface. Hradecky (1983) stated that the cord of these animals measures usually less than 20 cm.

Cross section of term umbilical cord with two arteries, two veins and allantoic duct above center.

Term cord near abdominal surface, with partial cover of fetal skin (above) and allantoic duct (below, center).

Allantoic duct accompanied by small amount of bladder musculature and small blood vessels.

7) Uteroplacental circulation

No details have been published.

8) Extraplacental membranes

Hradecky (1983) found small hippomanes in gnus; I have not found these allantoic residues in my specimens.

9) Trophoblast external to barrier

There is no trophoblastic infiltration of the uterus or endometrium.

10) Endometrium

The uterus is bicornuate with a single cervix but deep division by the uterine septum (Hradecky, 1982). There are four distinct rows of caruncles, best seen in neonatal uteri. Here they are moderately edematous and lack glands. The septa between villi are irregular and lined by a "syncytial epithelium" (Hradecky, 1988).

Two cross sections through a neonatal uterus with four pale caruncles each.

Higher magnification of endometrial caruncles in neonate.

11) Various features

There are no special features worth noting. There is no subplacenta and there are no "metrial glands".

12) Endocrinology

As in other ungulates, the placenta contains an abundance of binucleate cells, thought to be responsible for placental lactogen production. The origin and the multitude of lactogenic hormones have been discussed in detail by Forsyth (1986). Neonatal testes had no interstitial cell stimulation. The adrenal glands have conspicuously large medullary regions.

13) Genetics

Both species have 58 chromosomes of identical shape, all acrocentrics except for the largest chromosome, a submetacentric element (Wurster & Benirschke, 1968; Hsu & Benirschke, 1971, 1974). Corbet & Robinson (1991) also found no structural chromosomal differences between the two species when employing more advanced banding techniques. They arrived at a divergence time of 1 Million years from restriction fragment analysis of mtDNA. They were astonished at the low heterogeneity in the population, much like Grobler & v.d. Bank (1993). These authors studied the polymorphism of 33 protein loci in three populations and determined that most polymorphism existed in a population with 200 founders. They emphasized heterogeneity as an important management tools for game ranches. Ralls et al. (1979) had shown from captive populations that 85.7% of non-inbred offspring survived until 6 months, while only 70.7% of inbreds did. Gray (1972) reported on two putative hybrids between these species. One of these was from Hagenbeck Zoo and reported in detail by Zukowsky (1967). The animal came from a ranch in South Africa and had external features that betrayed its hybrid status. It lived to 26-28 months and had cranial features that were also intermediate between the two species. The other was at Zürich Zoo and then went to Leipzig without further details available. Their reproductive tracts were not reported.

Karyotypes of white-tailed gnu, Connochaetes gnou.

14) Immunology

I am not aware of any immunological studies other than the search for antibodies to viruses.

15) Pathological features

An outstanding consideration of gnu pathology is their carrier state for the virus of malignant catarrhal fever (alcelaphine herpesvirus 1 - AHV1). This infection has caused many problems in zoological parks (Metzler, 1991; Flach et al., 2002) and has been differentiated from the virus of sheep association. Rossiter et al. (1983) attempted to identify the virus from delivered placentas and suggested that it is rapidly inactivated by sunlight. It is probable, however, that calving and the simultaneous presence of the virus is related to infection of livestock at that time. Neonatal diarrhea is sometimes due to rotavirus infection (Baumeister et al., 1983). Anaplasma marginale was identified in gnus but apparently has no pathologic sequelae (Kuttler, 1984). Boomker et al. (2000) enumerated the parasites identified from a variety of South African ungulates. Peter et al. (1998) infected animals with the agent causing heartwater disease (Cowdria ruminantium) and established the importance of the tick (Amblyomma hebraceum) in the endemic areas. In his experience with numerous gnus at the San Diego Zoo, Griner (1983) found neonatal trauma or malnutrition as principal causes of death, with rare infections. He also noted that many blood vessels had irregular calcifications.

16) Physiologic data

Watson (1976) reported on electroejaculation, semen characteristics and preservation of semen. Basic hematologic values were provided by the study of Peinado et al. (1999).

17) Other resources

Numerous fibroblast cell lines of both species are available from the "Frozen Zoo" at CRES at the San Diego Zoo by contacting Dr. Oliver Ryder (oryder@ucsd.edu).

18) Other remarks - What additional Information is needed?

Early stages of implantation are missing and there are no details on gestational endocrine profiles.

Acknowledgement

The animal photographs in this chapter come from the Zoological Society of San Diego.