1) General Zoological Data
This large antelope, often called the blue buck, once occupied large regions of Pakistan, India and Nepal, but the range has recently contracted. Its first fossil record is from 18.5 MYA (Vrba & Schaller, 2000). The animals are frequently exhibited in zoological gardens and have done well in captivity. Since the release of 4.8 animals in Texas, a huge herd has developed there. Now, as many nilgai may live in Texas as there are left in their original habitat of Asia (Nowak, 1999). Males are darker, have short horns, a tuft on their necks, and they are larger (240-300 kg), while females are about 170 kg. Neonates weigh around 5.8 kg. First births are between 2 and 3 years of age. Longevity is 21 years and 8 months, according to Jones (1993).
Three studies of DNA have been performed to fathom the relationship of nilgai antelopes to other bovidae. Modi et al. (1996) studied repeated DNA families of 46 artiodactyl species and concluded from the findings that the subfamily Bovinae (including the Boselaphini, Bovini and Tragelaphini) was monophyletic. Matthee & Davis (2001) came to similar conclusions by studying nuclear DNA fragments. Hassanin & Douzery (1999) examined the mtDNA of the cytochrome b gene of 51 bovid species and concluded that the subfamily Bovinae includes four separate tribes, one of which is the Boselaphini.
|Nilgai antelopes at San Diego Zoo.|
General Gestational Data
Nilgai usually have twins, rarely triplets. In the United States, most are born in the fall (September/October), after mating in the preceding December. The gestation lasts 243-247 days. Estrus lasts 4 days.
General Characterization of the Placenta
|Pregnant uteri with immature twins.|
|Singleton fetus with vascular uterine supply and cervices.|
|Immature twin fetuses in the bicornuate (duplex) uterus. Note cord insertions. Traumatic hemorrhage is seen in the left placenta.|
|Placenta implanted in one of the uterine horns of the twin gestation. Note the irregular arrangement of the cotyledons.|
|Placenta of one twin peeled from the uterine horn.|
other two uteri came from a post partum female and one from an adult but
nonpregnant nulliparous dam. They are depicted below. Only in the youngest
animal was there an obviously linear arrangement of the caruncles. Nevertheless,
no "rows" could be enumerated and random sections through this
immature uterus shows perhaps as many as six caruncles. The large size
of uterine arteries supplying the endometrium is impressive. The post
partum uterus contained green, mucoid secretions. The caruncles were involuted
and had slightly hemorrhagic centers. Histologically, the endometrium
was focally hemorrhagic and edematous. Occasional remains of detached
villi were present in some glands, attended by mild lymphocytic infiltration.
An additional full term macerated fetus (3.5 kg, 45 cm CR length) with its placenta was available. It came from an injured dam that must have been in the process of delivery before death. The severely macerated fetus was apparently at full-term in April. This occurred in San Diego, however, where young are expected in the fall. Remarkably, one ovary had two active corpora lutea, while the other (of the nonpregnant horn's side) had a fibrotic corpus luteum. This is unlike the ovaries in the other two gestations.
Details of fetal/maternal barrier
|Three cotyledons of the twins' placenta (older gestation) with scant brown pigment accumulation shown at the arrows.|
|Edge of nilgai cotyledon with minimal pigment in trophoblast below chorionic plate. Note the degenerating material beneath.|
|Cotyledons of the younger, singleton pregnancy with minor hemorrhages and distended vessels at the same location as the previously shown pigment deposits.|
|Edge of cotyledon to show the degenerating maternal tissue between tips of villi.|
|The same photograph, cleaned slightly to reveal the writing. B.N.=binucleate cell.|
|Immature nilgai placental cotyledon with its right margin fully displayed.|
|Two adjacent cotyledons and the umbilical cord with its central allantoic duct.|
|Complete cotyledon of the immature twin gestation with adjacent uterine wall.|
|Implantation of villi within the white spaces of endometrium. They interdigitate with the endometrial caruncular epithelium but they do not invade.|
|Implantation site of nilgai placenta shows a sharp delimitation of fetal and maternal cells. The trophoblast remains on the villous surfaces, and is not invasive into the fibrous endometrial stroma. Endometrial glands underlie the entire cotyledon.|
|Higher magnification of the villous structure of the immature nilgai placenta as it is intertwined with the maternal septa. Binucleate cell shown at arrow.|
|The edge of a cotyledon shows the endometrial surface and degenerative debris, some of which results in the pigmentation of the trophoblast at the edges of cotyledons.|
|Trophoblast below chorionic plate with huge giant cells.|
|Trophoblast below the chorionic plate with pigment granules and fetal blood vessels above.|
|Similar view as preceding photograph.|
The umbilical cord lengths of these immature fetuses were 9, 8, 5 cm respectively. They were not coiled and were diffusely covered with fine granules. The cords contained 4 blood vessels and a central allantoic duct. The epithelium of the allantoic ducts is very thin and of urothelial type. One cord had the usual fine blood vessels, the other had none. The granules on the surface of the umbilical cord are fine squamous metaplastic foci.
|The surfaces of the umbilical cords have fine granules of squamous metaplasia.|
|The allantoic duct of the left umbilical cord is accompanied by very small blood vessels; the one below (left) is not.|
|The allantoic duct of the left umbilical cord (above left) is accompanied by very small blood vessels; the one on the left is not.|
There are no published studies, but the general architecture of the arterial arcades that supply the uterus can be seen in the singleton gestation depicted above.
Trophoblast external to barrier
|Uterus of singleton nilgai gestation with its placenta having been peeled away. Note the small (left) non-pregnant horn and the irregular arrangement of the caruncles.|
|Non-pregnant horn of the singleton nilgai gestation to show the mucus-covered caruncles.|
|Caruncle of unstimulated horn in the singleton gestation. Note the infiltration of endometrial glands (blue) from below.|
|Two uterine caruncles of the nulliparous female. Note the prominent arterial supply.|
There are neither subplacenta nor other notable features.
|Ovaries of singleton gestation. Atrophic-appearing ovary of unused horn (left) and numerous "corpora lutea" in the right ovary.|
|Both ovaries of the twin-bearing female had these numerous stimulated corpora. Which is the active corpus luteum could not be ascertained.|
|The ovary of the unstimulated side of the singleton nilgai gestation.|
the twin pregnancy, both ovaries had numerous equal-sized red "corpora
lutea" without any clear differences and no obviously larger one to
denote the CL of pregnancy. The ovary belonging to the immature singleton's
pregnant uterine horn was similar, with many corpora, while the other, non-pregnant
side was totally unstimulated. This inactivity may be the result of a diminished
utero-ovarian circulation of the non-pregnant horn, as suggested by Bill
Lasley (personal communication). Alternatively, it is possible that only
one ovary is stimulated when singletons result, much as in cetacea and in
a few other ungulates. Nevertheless, as can be seen from the preceding picture,
follicular development progressing normally just not corpora lutea. Moreover,
as indicated above, the macerated stillborn term gestation had two corpora
lutea on the pregnant side, and a fibrotic CL on the empty side. Obviously,
the hormonal milieu that leads to this ovarian histology is far from clear
at this time.
The fetal ovaries and testes showed no endocrine activity.
|Thick mucus (blue) normally fills the endocervical canal.|
Cell strains of numerous animals are available from CRES at the Zoological Society of San Diego by requesting them from Dr. Oliver Ryder at email@example.com.
Other remarks - What additional Information is needed?
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