Comparative Placentation

(Clicking on the thumbnail images below will launch a new window and a larger version of the thumbnail.)

Last updated
Nov 21, 2010

Topi & Sassabies
Damaliscus lunatus korrigum

Order:Artiodactyla
Family:Bovidae

1) General Zoological Data

Topis belong to a group of antelopes with curved horns, and the horns are present in both sexes. As a group, these animals are commonly referred to as "Sassabies" (Damaliscus sp.). The group contains three species and perhaps as many as seven subspecies that differ in coloration and size, as well as in chromosomal numbers. In addition to the Topi are the hartebeest (Alcelaphus buselaphus), and bontebok (and the blesbok - Damliscus dorcas, alias hunteri), with some subspecies (Nowak, 1999). Bonteboks in zoological parks are probably not a homogeneous group of animals, probably composed of hybrids between true bonteboks (from that park) with blesboks. It should be emphasized here that there has been considerable dispute of the nomenclature concerning their species designations (see Rookmaker, 1991, and Kumamoto et al., 1996). This is further discussed with respect to the chromosomal patterns under the section on Genetics.

Topis are the most abundant animals of this group of East African antelopes. They weigh around 100 + kg as adults and have strictly defended territories. The growth rate for one topi (Damaliscus korrigum [D. lunatus korrigum]) was charted by Hutchison (1970a). It attained a weight of 132.5 kg at 30 months. The gestational length is about 7-8 months with a single calf being born. Their longevity in captivity is around 20 years. Some subspecies are now very severely endangered and are, therefore, listed as CITES I species.

		Topi at San Diego Wild Animal Park.

		Two closely related species with dissimilar coloration and stature.

Many Sassabies are kept in numerous zoos and they have bred well there.

2) General Gestational Data

The length of gestation is given as 7-8 months, with singletons the rule. The bontebok has a gestation of 223-235 days and neonatal weight is 4.2-9.1 kg (average 7.1kg). Females are mature at 2 years. Topis have a gestational length of 229-231 days and weigh at birth 9.35 kg (Puschmann, 1989). Twins are most exceptional. Estrus follows birth in 5-8 weeks. Bonteboks are believed to live 15 years, blesboks 21 years, and topis 9 years.

3) Implantation

The topi and related species have a polycotyledonary, epitheliochorial placentation. The timing of implantation has not been reported.

4) General Characterization of the Placenta

		Cross section of a partial cotyledon from a delivered placenta with disrupted maternal floor (inside). Chorion on top.

		Section of immature, delivered placenta. Chorion on top.

The topi placenta is polycotyledonary; the placenta studied by me had 40 cotyledons that were arranged in four parallel rows. That placenta was from an immature pregnancy in the third trimester of gestation. It came from a dam that died with pneumonia, in January. The entire uterus, fetus with placenta included, weighed 11,575 g. The male fetus weighed 5,450 g and measured 54 cm in length. The placenta weighed 1,550 g; the uterus weighed 1,150 g; the remainder was fluid. The intact, but opened specimen is illustrated at the end of the chapter, under Pathology. Only one uterine horn was occupied by the placenta. Another specimen of Damaliscus l. korrigum had 50 cotyledons, weighed 1,300 g, and came from a Cesarean section after which the dam died.

In June, 2004, another topi placenta of a term live birth became available. It weighed 1,750 g, had 83 flat cotyledons that were arranged in four rows. They measured up to 12 cm in diameter and 0.5 cm in thickness. The umbilical cord measured 10 cm in length and contained 4 vessels and the allantoic duct. That placenta is shown next.

Delivered placenta of topi with 83 cotyledons in four rows.

The immature placenta of a stillborn blesbok had 30 cotyledons (5 x 2 x 0.5 cm), and weighed only 250 g. It was associated with a 500 g female embryo. In May, 2005 another stillborn with placenta was studied. The female calf weighed 1,900 g, was slightly macerated and accompanied by a 650 g placenta. It had 39 cotyledons, the largest of which was 8 cm in diameter. The umbilical cord had four vessels and measured 9 cm in length. Tiny caruncles of squamous metaplasia were present in its surface.

One bontebok placenta that I observed came from a term pregnancy that ended in neonatal demise after Cesarean section for dystocia. The cotyledonary mass consisted of 71 cotyledons and weighed 830 g. It had a 10 cm umbilical cord with two arteries, two veins, and a large allantoic duct. Another bontebok placenta had marked inflammation and will be discussed in the section on Pathology. Finally, a bontebok placenta made available on 11/18/2010 had 72 cotyledons and its umbilical cord measured 30 cm in length. It is shown next.


		New Bontebok placenta with 72 cotyledons arranged in rows.

		Uterus with placental sac exteriorized.

		Uterus after removal of the placenta showed the four rows of caruncles.

		The placenta after removal from the uterus, showing the cotyledons arranged in basically four rows.

5) Details of fetal/maternal barrier

The epithelium of the sparsely branched villi is similar to that of the many bovid placentas presented in this book. It is cuboidal and interrupted with binucleate cells. These are not so abundant as I found them in many other species, e.g. bongo, sheep. The binucleate cells are more numerous at the tips of the villi. The floor of the placenta is usually disrupted and difficult to describe for that reason. I have had only one specimen available that was attached to the uterus, but it was significantly autolyzed.

In some placentas, old hematomas with hemosiderin are found beneath the chorionic plate. In this new topi placenta, pigment if also found beneath the Chorionic plate, mostly associated with trophoblast. But, as in most other species, it does not stain with the Prussian blue reaction.

		Cotyledon of new topi placenta.

		Delivered topi placenta. The maternal floor is disrupted. The chorion is at top.

		Bontebok placenta at term, edematous perhaps due to prolonged labor and dystocia.

		Topi placenta attached to uterus, autolyzed. Note the endometrial glands.

		Bontebok placenta with old hematoma beneath chorion.

		Bontebok trophoblastic surface of villi with binucleate cell.

6) Umbilical cord

The umbilical cord of this specimen (the macroscopic features are described under Pathology below) was 12 cm in length. It had very small verrucae; and this, as all other sassaby cords, contained four blood vessels and a large allantoic duct. They have no spirals. Numerous small blood vessels are found, primarily around the large allantoic duct. The verrucae are composed of areas of squamous metaplasia.

		Portion of umbilical cord with large vein at left and allantoic duct at right. Many small blood vessels are present, some surround the allantoic duct.

		The surface of the umbilical cord has areas of squamous metaplasia (arrows) that correspond to the verrucae.

7) Uteroplacental circulation

This has not been described.

8) Extraplacental membranes

The allantoic membranes of the first topi placenta were heavily vascularized and
contained hippomanes wit crystals. There were no remnants of vitelline structures.

		The thin membranes that separate amnionic and allantoic cavities.

		Hippomanes in allantoic sac with crystals (arrows) under polarized light.

9) Trophoblast external to barrier

Since no well-preserved, attached placenta has been observed, it is unknown how
deeply the trophoblast invades. It would be unusual, however, to assume that the
myometrium was infiltrated by trophoblast in these species.

10) Endometrium

		Partial section of neonatal uterus showing one caruncle and adjacent endometrial glands.

		Higher magnification of fetal endometrium with caruncle.

11) Various features

No knowledge exists as to the presence of subplacenta or metrial glands. No true
decidualization occurs.

12) Endocrinology

We have not done any endocrine studies in these species and I know of no literature. The testes of neonatal deaths had no testicular interstitial cell stimulation.

13) Genetics

The topi (Damaliscus lunatus jimela) has 36 chromosomes (Kumamoto et al., 1996). This publication summarizes the complex chromosomal rearrangements and the nomenclature of the various Damaliscus species. The blesbok (Damaliscus pygargus phillipsi) has 38 chromosomes (Wurster & Benirschke, 1968). The bontebok (Damaliscus pygargus pygargus) has 38 chromosomes; the "hirola" or Hunter's hartebeest (Damaliscus [Beatragus] hunteri) has 44 chromosomes, but the NF (fundamental number) is the same in all, NF=60. The principal rearrangements found can be attributed to Robertsonian fusions. These papers contain an extensive discussion of the prior literature on these uncommon antelopes.

Hybrids have been reported between blesbok and bontebok, and between Cape hartebeest and blesbok. An alleged hybrid between a Cape hartebeest and topi has also been reported (Gray, 1972). Nothing is known about the fertility of the latter hybrids. The bontebok x blesbok hybrids produce normal fetuses.

14) Immunology

I know no studies.

15) Pathological features

While the San Diego Zoo has had excellent breeding results with topis, some
deaths have occurred and were discussed by Griner (1983). These were mostly due to "stress" with "white muscle disease" and trauma. Occasional bacterial infections were also seen, as in the dam whose fetus is illustrated next. This dam did not go into normal labor when she was at term gestation. She was immobilized and the fetus rotated. It died during extraction. The male fetus weighed 8.84 kg and was normal, showing no evidence of infection. The placenta had widespread foci of villous necrosis and inflammation. Branching fungi were identified on PAS stains, but they were not cultured and identified. The dam did well.

There were no neoplastic lesions in Griner's survey.

		Placenta with fetus in amnion after the allantoic fluid has been released.

		Fetus exteriorized with small amnionic sac collapsed. Other uterine horn below.

		Infected bontebok placenta at term with heavy leukocytic infiltration of villi, and necrosis (left).

		Higher power view of inflamed stem villi.

		Necrotic, inflamed villus in term bontebok placenta.

		Cluster of branching fungi in term bontebok placenta (PAS).

	16) Physiologic data Hutchison (1970b) paid special attention to the growth of topis when they are being reared artificially on milk and discussed the frequent failures. Hofman (1989) has presented a detailed analysis of the adaptation of the digestive system of these and related species to their different food preferences. 17) Other resources Cell strains are available from CRES at the Zoological Society of San Diego. 18) Other remarks - What additional Information is needed? Information on the placental/uterine interface is needed. Endocrine data should be collected. Acknowledgement Most of the animal photographs in these chapters come from the Zoological Society of San Diego. I appreciate also very much the help of the pathologists at the San Diego Zoo. References Gray, A.P.: Mammalian Hybrids. A Check-list with Bibliography. 2nd edition. Commonwealth Agricultural Bureaux Farnham Royal, Slough, England, 1972. Griner, L.A.: Pathology of Zoo Animals. Zoological Society of San Diego, 1983. Hofman, R.R.: Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system. Oecologia 78:443-457, 1989. Hutchison, M.: Observations on the growth rate and development of some East African antelopes. J. Zool. 431-436, 1970a. Hutchison, M.: Artificial rearing of some East African antelopes. J. Zool. London 161:437-442, 1970b. Kumamoto, A.T., Charter, S.J., Houck, M.L. and Frahm, M.: Chromosomes of Damaliscus (Artiodactyla, Bovidae): simple and complex centric fusion rearrangements. Chromosome Research 4:614-621, 1996. Nowak, R.M.: Walker's Mammals of the World. 6th ed. The Johns Hopkins Press, Baltimore, 1999. Puschmann, W.: Zootierhaltung. Vol. 2, Säugetiere. VEB Deutscher Landwirtschafts-Verlag, Berlin, 1989. Rookmaker, L.C.: The scientific name of the Bontebok. Z. Säugetierk. 56:190-191, 1991. Wurster, D.H. and Benirschke, K.: Chromosome studies in the superfamily Bovoidea. Chromosoma 25:152-171, 1968.