THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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ePithelium and binuc'reate ceJ'rs. Durlng the 5th and 6th weeks (35
,,;¿:,,ì"I
to 42 days) of development, the binucleate ce.lls are the predominant
ce1'l type in the apical regions of the chorionic v.l.l li.
An important feature of the chorionic virti of the pìacentome
in the later stages of gestation (after the 100 days) is the invaslon
of the co]umnar trophobrast by chori o-ar r antoi c capiìraries. In this
Process' which is not observed at any stage in the J ntercotyr edonary
zone, the caplllaríes become deeply invaglnated lnto the chorlonic
epithelium whose cells are inilmately molded on to them.
The placentomes are 60 to 100 ln number in the sheep
but show great variat.ion in size and shape. The placentomes of the
sheep increase ln size and number up to about the 90th day after whichthey
shrJnk with some possible decrease in number.
The I ntercotyl edonary zone of the sheep p.lacenta comprises:
the remalning part of the chorionic sac not involved in the fonnation
of the placentomes. It shows regionaì thickenings ln re]ation to the
pits which receive the mouths of the uterine grand; these are so-calred
"areolae" in which the chorionic epitheìium .is specialized for absorptìon.
The length of gestational period in the sheep is 145_l5b days.
. The above accounts are based on the works of !JÍmsalt(ls5.l'),
A¡noroso(t952), Davies(1952), Asdell (.l946), Davies et aì (1966), Bjorkman
(ts0s¡, Boshler(1969), and Boshier et al(.l972).
(a) Progesterone
During the estrus, seÉúm iählês varied from 0.12 ng/ml (equivatent
to anestrus) to 2.0 nglml fron day l0 to 14. After mailng, pregnant and
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