|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.
appearance of tiger placenta, one of triplets.
Its zonary nature is apparent; membranes ruptured at right. At left is the intact amnion/chorion.
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.
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.
General characteristics of placenta
|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.
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.
|Cross-section of amnion (bottom) and allantois (top) with vessels in allantoic membrane.|
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.
Additional needs for data to be collected
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