Malay Chevrotain (Lesser Mouse Deer) Tragulus javanicus

Order: Artiodactyla

Family: Tragulidae

1) General Zoological Data

Tragulidae, chevrotains or mouse deer, comprise the water chevrotains of the genus Hyemoschus of Africa, the Indian spotted chevrotains of the genus Moschiola and the Asiatic chevrotains of the genus Tragulus. They represent an ancient group of ruminant species (Chikuni et al., 1995; Vrba & Schaller, 2000). The latter genus has two species (T. javanicus and T. napu) (Nowak, 1999). T. napuis depicted in the summary of San Diego Zoo's historical mammal description (Dolan & Killmar, 1989). The derivation of the words is as follows: "tragulus" (Gr. = goat). The word chevrotain derives from French: chèvre = a female goat (Gotch, 1979). The Malay chevrotain is the smallest artiodactyl described, weighing up to 8 kg, but more often it is 2.5 - 4.5 kg. Upper canines are strongly developed and they may live in captivity up to 16+ years (Jones, 1993). They are secretive, grazing animals and endangered species because of loss of habitat.

Tragulus javanicus in Tokyo Zoo.

2) General Gestational Data

Gestational length is described to be from 140 to 177 days, with usually a single young resulting that weighs around 375 g at birth. The specimen available comes from a pregnant animal that died in mid-pregnancy. The uterus was fixed in Bouin's solution, which is the reason for the yellow stain but which also provides the excellent fixation. The uterus measured 15 x 9 cm and contained a female fetus with a 7 cm CR length.

Uterus containing placenta and fetus.

3) Implantation

Implantation is shallow and occurs over both uterine horns. No cotyledons are formed as they are in other deer. Early stages have not been observed and timing of implantation is so far unknown. A single pregnant uterus of a mid-gestation was available for study.

A most detailed study of the placentation of this species has recently been published by Kimura et al. (2004) whose study relied on nine specimens.

Another section to show the layout of the uterus.

Opened uterus showing the absence of placental cotyledons.

Bicornuate uterus with fetus attached to short umbilical cord. Note the diffuse nature of the placenta.

4) General Characterization of the Placenta

In contrast to other deer, this animal does not possess placental cotyledons; it also shows no real villous structures, at least at this young age. The placenta is more similar to that of camels and pigs and was so described already by Turner (1876) and Garrod & Turner (1878). It is a more or less diffuse epitheliochorial placenta that extended over both uterine horns. Concave protuberances could be palpated on the fetal surface of the placenta.

5) Details of fetal/maternal barrier

This is a typical epitheliochorial placenta without trophoblast infiltration of the endometrium. The trophoblast stained strongly with cytokeratin and weakly with placental alkaline phosphatase (PALP) reactions. Binucleate trophoblastic cells are abundant and stained positively with antibodies against bovine placental lactogen. They also stained strongly with PAS. Fetal and maternal vessels stained strongly with vimentin.

Implanted placenta with endometrium bottom right.

Implantation site with endometrial glands below.

Cytokeratin staining of trophoblast.

Binucleate cells stained with anti-bovine lactogen.

6) Umbilical cord

The umbilical cord of this small fetus was 4 cm long and had 4 blood vessels in addition to the allantoic duct. It was also slightly spiraled.

Section of two vessels in the umbilical cord and edge of allantoic duct (above).

7) Uteroplacental circulation

These structures have not been studied in detail.

8) Extraplacental membranes

There is an elongated allantoic sac containing sparse blood vessels. The amnion has a single layer of squamous epithelium.

Allantoic membrane of chevrotain.

Chorionic membrane forming the arcades. Note also the binucleate cells.

9) Trophoblast external to barrier

No trophoblastic infiltration of endometrium or vessels occurs.

10) Endometrium

There is no decidua.

11) Various features

None.

12) Endocrinology

I am not aware of many endocrine studies having been done in this species. The presence of binucleate cells with positive reaction to bovine placental lactogen is in conformity with other ruminants (see Atkinson et al., 1993, and Wooding, 1982). The summary of deer endocrinology by Plotka (1999) does not include this species. Wallis & Wallis (2001) described the evolution of growth hormone in this species.

13) Genetics

The animals have 32 chromosomes with a large X-chromosome as shown below (Soma, unpublished; Gallagher et al., 1996; Liming & Yuze, 1989; Yong, 1973). The same findings were made in T. javanicus williamsoni. Hybrids have not been described. New molecular data that show the ancient origin of this Order, including lesser and larger mouse deer, have been provided by Chikuni et al. (1995). Cytochrome c gene sequences were studied by Irwin et al. (1991). Breukelman et al. (2001) discussed the phylogenetic sequence by studying secretory ribonucleases (RNases).

Karyotypes of Malay chevrotains.

14) Immunology

We are not aware of any relevant studies.

15) Pathological features

The only abnormal findings made in Malayan chevrotains were malnutrition (Griner, 1983), and in an African chevrotain Griner found glomerulosclerosis. Grondahl et al. (2003) found bovine diarrhea viruses in a Malay mouse deer. Ciliated parasites (Isotrichia jalaludinii) were identified in the stomach of lesser mouse deer by Imai et al. (1995).

16) Physiologic data

Mossman & Duke (1973) described a large thecal ovarian gland in mouse deer. These animals also possess the smallest erythrocytes of mammalian species. They are spherical and thus cause increased viscosity of blood despite which cardiac output etc. are within normal limits (Weathers & Snyder, 1977). Unique pits were observed in the red blood cells by Fukuta et al. (1996), using scanning EM. Electroejaculation and the semen obtained were published by Haron et al. (2000).

17) Other resources

Some fibroblast cell strains are available from CRES at the San Diego Zoo by contacting Dr. Oliver Ryder at oryder@ucsd.edu.

18) Other remarks - What additional Information is needed?

Early stages of implantation and measurements of term placentas and umbilical cord are needed.

Acknowledgement

The animal photograph in this chapter comes from Professor Hiroaki Soma. I am sincerely grateful for his contributing this placenta to this site (KB).

Tragulus javanicus in Tokyo Zoo. This animal was provided by the Malay Breeding Center, courtesy of Associate Prof. Junpei Kimura, Veterinary Department, Nihon University, Fujisawa, Kanagawa, Japan. Accordingly, I would like to acknowledge his kind cooperation.