Indochinese Tiger (Panthera tigris corbetti)

Order: Carnivora

Family: Felidae

1) General zoological data of species

Tigers have an Asiatic distribution, with several subspecies having been described. The animal shown here comes from Vietnam and it is one of the severely endangered subspecies. A few animals of this subspecies breed in the few zoological gardens that exhibit them. The reproductive physiology and placenta is deemed to be the same among all subspecies and similar to the domestic cat.

Indochinese tiger at San Diego Zoo.

2) General gestational data

The length of gestation in tigers is around 105 days; it is significantly shorter in the domestic cat (65 days) but, otherwise, they have some similarity in their placenta and reproductive parameters. The litter size varies but usually, two to four cubs are born. The newborn weight of one of our triplets whose placenta is shown here was 1,100 g. The maternal weight of tigers (not pregnant) is around 100 to 120 kg.

The placenta of this triplet weighed 250 g, with cord and membranes; the dam ate the other placentas of the triplets. One previous study of tiger placentas by Srivastava (1952) was unavailable to us.

External appearance of tiger placenta, one of triplets.

Its zonary nature is apparent; membranes ruptured at right. At left is the intact amnion/chorion.

Same placenta after opening; the forceps is inserted into the allantoic duct where the cord attaches to the placenta. At top right and below the cord insertion are the amnion and chorion. Below the forceps is a dark cluster of hippomanes.

3) Implantation

In the domestic cat, implantation occurs on day 12-14 post coitum and the trophoblast is superficially invasive (Leiser, 1979). The precise time of implantation is not known.

4) General characteristics of placenta

This is a zonary placenta that forms a complete ring around the uterus. There are two major subdivisions whose vascularization consists of two separate sets of blood vessels which originate from the umbilical cord.

There is a large allantoic sac and only very little marginal hematoma, much less than seen in canidae and some other carnivora. Mossman (1987) described the felid placenta as being endotheliochorial. Zhemkova (1962) took issue with this and declared that the cat placenta is hemochorial. Electron microscopic studies, however, did not confirm Zhemkova's opinion. In comparison with the domestic cat, the tiger placenta has a much denser and more complex structure.

The uterus of felids is bicornuate and both sides are used for implantation of the litters. The cord attaches laterally on the placental disk. The first implantation occurs antimesometrially. Leiser (1979) and Perry (1981) showed excellent photographs of early implantation in the cat.

Another placenta I had the opportunity to examine, of stillborn twin Sumatran tigers at term, provided the following data: male fetal weight 1,050 g; placental weight 275 g. Zonary placenta measured 30 cm in length, 10 cm circular, 0.5 cm in thickness, 3 cm long cord with 2 arteries, one vein and allantoic duct.

This species, as other felids, has a labyrinthine architecture of its villous tissue.

Placental labyrinth with maternal and fetal vessels.

Surface of tiger placenta with amnion and chorion above that contain some fetal blood vessels. The labyrinth is below.

Higher magnification of placental surface.

Maternal surface below, labyrinth above.

5) Details of barrier structure

The feline placenta is usually considered to have an endothelial-chorial barrier relation (Mossman, 1987; Ramsey, 1975, Wimsatt, 1962). Ludwig (1968), who likened the barrier to the nephropneumoid regions, also considered the feline placenta to be endotheliochorial. Wislocki (1920), using trypan blue, showed accumulation of the dye in the maternal endothelium but no transfer to the fetus. Nevertheless, a hemochorial nature of this barrier was suggested by Zhemkova (1962) who investigated Barr body identification of maternal and fetal layers, in placentas of male fetuses.

The fine structure of the placental membrane of the cat has been described by Wynn & Björkman (1968) and Leiser (1979). From these studies it is apparent that the domestic cat's placenta (and probably that of the tiger) have a maternal endothelium - thus, the appellation "endothelial-chorial" seems to be correct.

Fetal-maternal barrier of labyrinthine tiger placenta. The trophoblast borders maternal blood space; fetal vessel in center.

6) Umbilical cord

The umbilical cord measures approximately 10 cm in length. It has two sets of vessels (artery and vein) and a large central allantoic duct. The cord inserts marginally and has no twists. Much of the umbilical cord runs in the membranes before attaching to the fetus. Numerous smaller allantoic vessels are also present, and the allantoic duct may contain dark hippomanes.

Insertion of umbilical cord, before it extends to the right horizontally in the membranes. There are two sets of vessels and an allantoic duct.

Cross-section of umbilical cord with its large allantoic duct in the center. Placenta at left, large fetal vessel at right.

7) Uteroplacental circulation

No information is available.

8) Extraplacental membranes

The amnion develops by folding. Its epithelium is very thin. The allantois is vascularized and has flat or cylindrical epithelium. It also contains frequently dark brown hippomanes which include birefringent oxalates.

Cross-section of amnion (bottom) and allantois (top) with vessels in allantoic membrane.

Hippomanes.

9) Trophoblast external to barrier

No pregnant uterus has become available to ascertain the depth of trophoblastic invasion; if one assumes it to be similar to cats, then the myometrium is not infiltrated and only the endometrium has trophoblast, eroding the glands. No vascular invasion is demonstrable.

10) Endometrium

There is minimal decidualization.

11) Various features

None are described.

12) Endocrinology

Gonadotropins of pregnancy have not been described for tigers, and no information on other endocrine secretions has been published. There is much information on domestic cats, however (Please see the chapter on cat).

13) Genetics

Tigers have 38 chromosomes, as do the majority of Felids, except some of the South American species with 2n=36.

We have seen 39 chromosomes with XXY sex chromosomes ("Klinefelter Syndrome" - in humans) in an infertile but otherwise normal tiger. This (39,XXY) is a well-recognized error in domestic cats, where triploidy and chimerism are also common. We have also seen an autosomal trisomy in a fetus of a domestic cat.

Fertile hybridization among subspecies, and with lions occurs. Leopard x Tiger hybrids have aborted (Gray, 1972).

Genetic studies are restricted to the cat chromosomes. Murphy et al. (1999a) reported virtual complete conservation of the X-chromosome, including complete synteny) between cat and man. The Y chromosome was also exceedingly similar. Other genetic studies compare chromosome 12 and 22 (Murphy et al., 1999b). O'Brien et al. (1997) reviewed the evolution and comparative genomics of cats, but the tiger was not included. Other karyological studies can be found in the publications by Hsu & Rearden (1965), Roubin et al. (1973) and Wurster-Hill & Gray (1973). Newman et al. (1985) described electrophoretic biochemical variation among various felids, including tigers.

14) Immunology

MHC molecules, NK cells, and other immune cell populations have not been described.

15) Pathological features

Tigers are susceptible to a large variety of infectious organisms, much as cats are. We have seen cataracts, renal failure ("Tiger-Krankheit") and they have normally lipuria.

Habitually aborting domestic cats were studied by Huxtable et al. (1979) who found multifocal placental necrosis without identifying the cause of this lesion. The postpartum uterine involution of the domestic cat was described by Dawson (1946), and McEntee (1990) described other features of uterine and ovarian pathology. He also summarized the occasional uterine torsion in pregnancy and infections. In domestic cats, herpes virus infection leads to necrotizing placentitis and abortion (Hoover & Griesemer, 1971). Numerous genetic diseases have been described in cats (Migaki, 1982), but few (other than albinism) have been assigned to the tiger (Berrier et al., 1975).

16) Physiological data

There are no data on uterine blood flow, blood volume, or blood pressure. It is known, however, that tigers have lipuria (Hewer et al., 1948), a feature we have been able to confirm.

17) Other resources

Cell lines are available from the "Frozen zoo" of CRES at the Zoological Society of San Diego. A sweeping review of the phylogeny of felids comes from Thenius (1967).

18) Additional needs for data to be collected

Virtually no pathology has been recorded of pregnancies. But, the accidental finding of a 39,XXY tiger ("Klinefelter syndrome-equivalent") suggests that more studies of placentas and neonates could be useful.