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Placental and fetal development during multiple bovine pregnancy. Anatomical and physiological studies

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Placental and Fetal Development
during
Multiple Bovine Pregnancy
ANATOMICAL AND PHYSIOLOGICAL STUDIES 1n2r3
E. S. E. HAFEZ AND E. FAJAKOSKI*
Department of Animal Sciences, Washington State University,
Pullman, Washington
ABSTRACT
Cattle were injected with PMS, bred and slaughtered 3, 30, 45, 60 and
90 days after ovulation and the genital tracts dissected. From 30 to 90 days of pregnancy the percentage increase in the weight of single embryos was 85 times as much
as the increase in crown-rump length. The volume of amniotic fluid increased 580
times in the second month of pregnancy and increased twice during the third month of
pregnancy. The allantochorion did not lengthen between 60 and 90 days of pregnancy.
At 30 days of pregnancy there was no significant difference in the crown-rump length
or the weight of embryos of singles, twins, triplets, quadruplets or quintuplets. The
volume of placental fluid per embryo was higher in singles than in twins and triplets;
the volume of placental fluids per embryo decreased further in quadruplets and quintuplets. The weight of the placental membranes per embryo was heavier in singles than
in twins, triplets and quadruplets; the weight of membranes was markedly decreased
in quintuplets. The effects of overcrowding in utero on the conceptus was more
pronounced at 60 days than at 30 days and in quintuplets than in triplets and quadruplets. Anastomosis of vascular supply of allantochorions occurred as early as 30
days of pregnancy.
Extensive morphological studies have and Reece, '53). Interlocking between the
provided information on the development chorion and the maternal cotyledons does
of the trophoblast and the early embryol- not begin until the fortieth to fiftieth day
ogy of the cow during single pregnancy (Chang, '52). Before that time, the rela(Hammond, '27; Winters et id.,'42; Boyd tionship between the chorion and the endoet al., '44; and Hamilton and Laing, '46). metrium is more or less of a diffused epiWinters et al. ('42) described the first theliochorial placenta; during the second
stages of chorionic elongation in a 13-day month this begins to change to a cotyledonembryo. Chang ('52), studied embryos of ary placenta.
The development of the allantochorion
unknown age and observed an extremely
rapid growth of the trophoblast prior to in the cow is of particular interest. Essenan estimated age of 18 days. Such findings tially, the chorion is formed by elongation
were augmented by Greenstein, et al. ('58) of the trophoblast, which becomes invested
who attempted to define daily standards of with a layer of endodenn followed by the
normal variation and development for lateral development of the mesoderm. The
accurately timed embryos recovered 16 to allantois develops as an outgrowth of the
hind end of the gut, and rapidly elongates
26 days post coitum.
Other investigations have contributed and closely invests the chorion. The vasdata relative to the mode of placentation cularized allantois brings its blood vesseIs
in the cow. The data of Green ('46) may in close opposition with the chorion, so
indicate that the site of implantation of
the bovine blastocysts is determined at the
eleventh day. The allantochorion becomes
attached to the endometrial caruncles at
some 33 days of gestation. At 35 days this
attachment is firm enough for the embryo
to receive part of its nourishment through
the cotyledons (Melton et al., '51; Foley
ANAT. REC., 1 5 0 : 303-316.
303
304
E. S. E. HAFEZ AND E. RAJAKOSKI
forming the vascular allantochorion. Fusion is practically complete by the twentyeighth day (Amoroso, '58). In multiple
pregnancies the allantoida of embryos
elongate within the common trophoblast
and they commonly anastomose where
they meet.
The body proportions of the fetus change
markedly as gestation advances; some approximate the corresponding proportion of
the adult at one age, some at another. The
stage of gestation at which the bovine
fetus most nearly approximates the adult
in body proportions is 2 to 3 months for
ratio of height at withers to depth and
width of chest and 6 to 7 months for ratio
of height at withers to length of head
(Swett et al., '48).
Conspicuously absent from the literature
ture has been any detailed studies on the
developmental morphology of the placenta and fetus of a monotocous species
during induced multiple pregnancy. Such
a study is obviously vital to an understanding of the nature of the high incidence of
embryonic mortality during multiple pregnancy in cattle. This investigation was
made to study the effect of crowding in
utero on the developmental morphology
of the conceptus during early stages of
multiple pregnancy with special emphasis
given on the development of fetus, its internal organs and ossification centers.
dissected, and their lengths measured (fig.
1 ) . The lengths and diameters of the
gravid and non-gravid horns were recorded. The uterus was cut open from the
right uterotubal junction and the fetuses
were recovered and identified. The length
of allantochorion and necrotic tips, dimensions of amniotic vesicle, volume of amniotic and allantoic fluids, and weight of
amniotic membranes were measured. The
crown-rump length, umbilical cord length
and weight of fetuses were recorded. The
fetuses were immersed in warm saline to
judge their viability by heart beat. Degenerating and non-viable fetuses were not
considered and were excluded from the
data on fetal development. The fetuses
were cut open and the following glands
and organs were dissected from the adjacent connective tissues and weighed:
gonads, digestive tract (full), liver, kidneys, adrenals, lungs and heart.
Tissue clearing techniques
Eviscerated fetuses were fixed in 10%
formalin for at least 48 hours, cleared in
2% KOH solution for 7 to 10 days and
stained for two hours with Alizarin Red S
(1: 10,000 in 2% KOH). The specimens
were rinsed in several changes of distilled
water over a period of two hours and gradually dehydrated through a series of increasing concentrations of glycerol ( 1/4
glycerol: 3/4 H20: 1/2 glycerol; 1/2 H,O;
3/4 glycerol; 1/4 HzO: 1 glycerol) and
MATERIALS AND METHODS
then stored in a second or even third
Fifty nulliparous beef cattle heifers of change of glycerol. This gradual dehydraHereford breed aged one and one-half to tion was necessary to prevent shrinkage
two years were used. The heifers were and deformity of body shape. The specichecked twice daily for the incidence of mens were turned every few hours to inestrus with a vasectomized bull. On day 16 sure even clearing on all sides. Great care
(the day of estrus = day 1 ) each animal was taken to handle the fragile jelly-like
was injected with 1,500 to 2,000 i.u. of fetuses by supporting both the head and
PMS (Equinex, Ayerst) subcutaneously. At the body with rubber-gloved hands.
the following estrus the heifers were bred
Microscopic examination of
to a fertile bull and artificially inseminated
ossification centers
with frozen semen. Pregnancy was diagnosed by palpation per rectum.
Sixteen 60-day and six 90-day fetuses
were used to study the effect of sex and
Autopsy
litter size on ossification pattern. The
The animals were slaughtered 3, 30, 45, length and thickness of the following ossi60 and 90 days after ovulation ( f 12 hrs). fied bones were measured microscopically,
The genital tract was removed after using a calibrated ocular or calipers: manslaughter. The corpora lutea on each dible, scapula, tenth rib, ilium, femur,
ovary were counted, the uterine tubes were tibia, fibula, humerus, ulna and radius.
MULTIPLE PREGNANCY IN CATTLE
?I
305
TI
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I
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I
1I
e
I
I
I
I
I
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I
I
I
I
I
I
I
5
I
I
V
3
_ _ _ _h r _-_-_-_-4 ----- -----
+---- - ----- -----
,
Y
Fig. 1 Technique used to measure the dimensions of the reproductive organs and conceptus of experimental animals. a,b, length of gravid and non-gravid uterine horns; c,d,
width of uterine horns; e, length of uterine tubes; f, length and width of fimbriae; g, largest
dimension of ovary, length and width of corpus luteum; h, interamnion spaces; i, length of
allantochorion; j, length and width of amnion.
RESULTS
Morphology of reproductive organs and
conceptus during single pregnancy ovaries.
The dimension, volume and weight of
ovaries at 30 days of pregnancy were
higher than that at three days after ovulation. There were no significant changes
in these values from 30 to 90 days of
pregnancy (table 1). In general, ovary
weight was sigmficantly related to number of corpora lutea (fig. 2). The number
of unruptured follicles, over 10 mm, at
three days after ovulation ranged from
nil to 16 with an average of 3.4. Such
unruptured follicles seemed to regress
throughout later stages of pregnancy. The
diameter of corpus luteum at three days
after ovulation ranged from 11 to 14 mm
and the average was 12.3 mm. From 30
to 90 days of pregnancy the diameter of
corpus luteum vaned from 14 to 22 mm
with an overall average of 19.7 mm. At
three days after ovulation the weight of
corpus luteum, during early pregnancy,
fluctuated between 1,813 and 5,240 mg.
The stage of pregnancy from 30 to 90
days had no significant effect on the diameter or weight of the corpus luteum.
Reproductive tract. In all experimental
animals the length of the fimbriae ranged
from 44 to 84 mm with an overall average
of 68 mm. The width of fimbriae ranged
from 23 to 38 mm and averaged 30 mm.
The length of the uterine tube ranged from
15 to 25 cm and averaged 21 cm. The
stage of pregnancy had no significant
effect on the size of fimbriae or length of
uterine tube. The length of the uterine
horn during non-pregnancy varied from
22 to 34 cm with a mean of 27.0 cm.
The gravid horn lengthend progressively
throughout pregnancy and reached an
Stage of pregnancy (days)
3
453-820
Weight of corpus
luteum ( m g )
657
12.3
3.4
1.3
4.65
4.95
28.4
Mean
1813-5240
14-23
0-2
1-3
7.0-13.8
4.0-15.5
21-36
283
224-304
283
2.2
0-5
224-304
6-10
2
14
88-232
94-364
0-10
0-5
27-34
1.1
27
0-2
22-32
+
28-38
27.0
30
Range
22-34
Mean
Length of gravid horn (cm)
D B . in length
of both horns ( c m )
Diameter of gravid horn ( m m )
DifF. in diameter
of both horns ( m m )
Diff. in number of visible
caruncIes in both horns
Weight of uterus conceptus
+cervix (gm)
Weight of empty uterus
cervix ( g m )
3
Range
Stage of pregnancy (days)
Measurements
+
30
Range
TABLE 2
3605
19.1
0.7
1.5
9.19
9.83
29.7
Mean
45
23284686
17-21
0-5
1
4.6-6.6
3.5-9.0
23-35
Range
3470
19.3
19.8
2.0
1.5
10.5
13.0
35.7
Mean
2550-4970 3416
17-22
14
1-3
0.8
5.3-19.3
60
1.o
8-18
25-48
Range
5.91
6.11
29.5
Mean
45
181
203
385
-
8.8
1-16
7.0
244
11
6-16
10.3
37
40
8
~
Mean
7-13
32-41
35-46.5
Range
2.3
31
33.4
Mean
60
259-452
655-1092
3-9
10-31
1-9
60-75
4225
Range
343
829
2.5
20
6.0
67
43.7
Mean
90
19-22
0
1
6.7-10.2
8.5
2642
Range
20.5
0
1.o
8.25
8.5
34.1
Mean
417-640
1200-1820
4-12
35-85
8-18
90-135
37-50
Range
90
566
1600
7.2
62
13.0
115
45.0
Mean
3117-4570 3839
Differential developments in the morphology of the gravid and n o n gravid horns during single pregnancy
11-14
0-16
Diameter of corpus
luteum ( m m )
Number of unruptured
follicles (over 10 m m )
3.3-6.4
Weight ( g m )
1-2
2.8-6.5
Volume ( m l )
Number of corpora lutea
22-35
Range
Largest diameter ( m m )
Measurements
TABLE 1
Developmental changes i n morphology of ovaries duTing single pregnancy
307
MULTIPLE PREGNANCY IN CATTLE
80
-
70
-
60
-
E50
-
6
v
t
c
rn
40
-
3
2
? 30 -
3 0 Days P r e g n a n c y
0
20
-
10
-
a;:@
:
01
@
'
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I
0
2
4
6
8
I
10
I
I
12
14
I
16
18
20
I
22
Number Of Ovulation I n O v a r y
Fig. 2 Relationship between ovarian weight and number of ovulations at 30 days of pregnancy.
average of 45.0 cm at 90 days of pregnancy
(table 2). The average difference in length
of non-gravid and gravid uterine horns was
2.3 cm at 30 days of pregnancy and 13.0
cm at 90 days. The diameter of the uterine
horn during non pregnancy ranged from
22 to 32 mm with an average of 27 mm.
The diameter of the gravid uterine horn
increased progressively throughout pregnancy and reached an average of 115 mm
at 90 days of pregnancy. Difference in the
diameter of gravid and non-gravid horns
was first noted at 30 days of pregnancy.
Each uterine horn during non pregnancy
had 43 to 72 visible caruncles; the gravid
horn had a few more visible caruncles.
The percentage increase in weight of
uterus and conceptus was greater in the
second month of pregnancy than in the
first and third.
Embryos. The crown-rump length of
30-day embryos varied from 8.1 to 12.5 mm
with an average of 10.0 mm. The average
crown-rump lengths of 45-, 60-, and 90-day
fetuses were 28.0, 74.3 and 159.3 mm
respectively. The weight of 30-day embryos
ranged from 69 to 178 mg with an average
of 114 mg. The average weights of 45-,
60-, and 90-day fetuses were 2.0, 16.8 and
156.8 gm respectively. From 30 to 90 days
of pregnancy the percentage increase in
the weight of embryo was on an average
85 times as much as the increase in crownrump length. The average length of umbilical cord was 2.5 cm at 60 days of pregnancy and 6.5 cm at 90 days.
Placenta. The average length of amniotic vesicle at 45, 60 and 90 days was 3.9,
9.4 and 32.7 cm respectively. At 30 days
of pregnancy, the volume of amniotic
fluid was 0.1 to 0.2 ml; this fluid increased
570 times in the second month of pregnancy and increased twice during the third
month of pregnancy. The percentage increase in the volume of allantoic fluid was
much slower than in the amniotic fluid.
The ratio between the volume of amniotic
fluid: volume of allantoic fluid at 45, 60
and 90 days of pregnancy was 1:16, 1:3
and 1:4 respectively.
308
E. S. E. HAFEZ AND E. RAJAKOSKI
60
DAY
-
90
DAY
I
.
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.
1
40
0
---
.
1
80
1
.
I
120
Lenqfh of ollontochorion fcm)
Embryo or fetus
-. Allontrochorion
Necrotic tip
Fig. 3 Diagram of the pattern of spacing of embryos along the allantochorion during
multiple pregnancy at 60 and 90 days of gestation in cattle. The length of allantochorion
is drawn to scale and the width of the amnion is not considered. Note the uneven spacing
of the fetuses along the allantochorion and the shorter placenta at 90 days as compared to
that at 60 days.
There was no increase in the length of
the allantochorion between 60 and 90 days
of pregnancy (fig. 3). At 30 days of pregnancy the weight of the amnion and
allantochorion ranged from 0.59 to 3.77
gm with an average of 1.81 gm. The relative increase in the weight of placental
membranes was much slower in the third
month of pregnancy than in the second
month, whereas the relative increase in
fetal weight was much higher in the third
month (fig. 4).
ERect of litter size on weight
of embryos a n d placenta
At 30 days of pregnancy there was no
significant difference in the crown-rump
lengths or the weights of embryos of singles, twins, triplets, quadruplets or quintuplets (table 4). The volume of placental
fluid per embryo was significantly higher
in singles than in twins and triplets; the
volume of placental fluids was decreased
further in quadruplets and quintuplets.
The weight of the placental membranes
per embryo was heavier in singles than
in twins, triplets and quadruplets; the
weight of membranes was markedly decreased in quintuplets.
At 60 days of pregnancy there was a
slight increase in the crown-rump length
and weight of embryos of singles as compared to twins and triplets. Assuming that
sex differences in fetal weight exist at 60
days of pregnancy, there is evidence to
indicate that overcrowding in utero reduced weight of viable fetuses (fig. 5). Unlike the results at 30 days of pregnancy
there were no significant differences between the volumes of placental fluids at 90
days in singles, twins and triplets. Litter
size exerted a reducing effect on the weight
of placental membranes.
The effects of overcrowding in utero on
the components of the conceptus was more
pronounced at 90 days than at 60 days of
MULTIPLE PREGNANCY
309
IN CATTLE
140,000
I20,OOO
a
0
100,000
m
Ea
0
M
t
0
Em
60,000
.-
P
0
t
Q)
40,000
?
0
.-r
20,000
Membranes
0
30
60
90
Stage of Pregnancy (days)
Fig. 4 Relative increase in components of conceptus (fetus and placenta) at 45 to 90
days of pregnancy as compared to that at 30 days in single pregnancy. Note the high rate
of increase in fetal weight and low rate of increase in placental weight during the third
month of gestation.
gestation and in quintuplets than in triplets and quadruplets (fig. 6). At 30 days
of pregnancy, the adjacent placentae were
either separated by necrotic tips or were
completely or partially envaginated (fig. 7).
Necrotic tips between adjacent allantochorions were found in some twin and
triple pregnancy (fig. 8). Anastomosis of
vascular supply of allantochorions occurred as early as 30 days of pregnancy.
E. S. E. H A F E Z AND E. RAJAKOSKI
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Effect o f litter size and sex of fetus
on development o f organs and
ossification centers
In 60-day fetuses the weight of major
internal organs was not significantly affected by litter size (table 5). There were
no significant differences in organ weights
of males and females in 60- and 90-day
fetuses. The weight of a single fetus at
90 days of pregnancy was approximately
11 times its weight at 60 days and it
seemed that the internal organs had developed at a similar rate from 60 to 90
days of single pregnancy.
I n 60-day fetuses, the following bones
were ossified and readily stained by the
Alizarin Red S: mandible, scapula, ribs,
ilium, femur, tibia, fibula and metacarpus.
The ischium, however, was not well ossified to be stained with Alizarin Red. The
dimension of the ossified bones did not
differ significantly between singles, twins
and triplets of 60-day fetuses (table 6).
Also, there were no significant differences
between dimensions of ossified bones of
males and females in 60- and 90-day
fetuses. There was no evidence to show
that the growth rate, between 60 and 90
days of gestation, is higher for some bones
than for others (fig. 9).
Fig. 5 Gravid uteri cut open to show the degree of development of endometrial caruncles in
relation to number of implantations at 60 days of
gestation. Note the effect of crowding in utero
on fetal weight.
a (102) Triplets: Two implantations, evenIy
spaced in the right uterine horn and one in the
left horn. The two fetuses in the right horn
weighed 14.21 (d) and 14.88 gm ( 8 ) whereas
the single fetus in left horn weighed 15.38 gm
( 9 ) . Note a similar degree of development of
caruncles in both horns.
b (103) Twins: Two implantations (see two
arrows) in the right horn; the fetuses weighed
14.58 ( 9 ) and 15.48 gm ( 8 ) . There were n o
implantations in the left horn but the allantochorion migrated from the right horn to half the
length of the left horn (see arrow). The caruncles and the fetal-maternal attachments were
well developed in the right horn whereas the caruncles were only eroded in the left horn.
c (97) Twins: Two implantations in the right
horn, the fetuses weighing 12.45 ( 0 ) and 13.49
gm (d). Note the lack of development of caruncles in the left side which was a blind uterine
horn; the allantochorion was confined to the right
horn only. The fetuses in this case were lighter
than in "b" (cow with a double cervix).
(All implantations were represented by viable
fetuses.)
MULTIPLE PREGNANCY IN CATTLE
Figure 5
311
E. S . E. H A F E Z A N D E. RAJAKOSKI
DISCUSSION
m w e m m
c - e c o w e
3.3.3.3.3.
0 0 0 0 0
&
& i d &
w m o o w
99??9
0 0 0 0 0
E
v1
+lo
O R
02
Z 8
aJw
u
g;.
I4
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co
The relative growth of the different components of the gravid uterus during early
gestation is correlated with functional
necessity. After implantation, the allantochorion develops faster than other parts of
the conceptus : this is achieved by "creep"
growth through the non-gravid horn. Following the rapid growth of the placental
membranes, the fetal fluids increase rapidly; the distension of the blastocyst
presses the trophoblast cells firmly against
the uterine mucosa and so allows the intimate contact between fetal and maternal
cotelydons. The fetal weight increases very
slowly during early stages of gestation,
but rapidly late in gestation. Similar patterns in the differential growth of the
conceptus take place in other species
(Malan and Curson, '37; Wallace, '48;
Huggett and Hammond, '58).
The periods of morphological changes of
the developing embryo are preceded by developmentally adaptive stages aimed to
supply the developing organism with nutritional requirements including oxygen.
Smidt ('51 ) characterized six prenatal
stages in cattle : ( 1) intracellular nutrition
and anaerobic respiration 1 to 12 days
after fertilization: ( 2 ) nutrition through
the trophoblast, 12 to 15 days: ( 3 ) nutrition through the trophoblast and yolk sac,
16 to 2 1 days: ( 4 ) the allantois, in close
association with the chorion, 22 to 27 days:
(5) the allantochorion with its primitive
cotyledons 27 to 50 days: and ( 6 ) the
complex cotyledons of the placenta, 51 to
280 days. During multiple pregnancy the
number and size of eroded caruncles are
greater than in single pregnancy. The
surface area of eroded caruncles corresponds to litter size. It is not known
whether the surface area of fetal-maternal
attachment, the eroded caruncles, is correlated with fetal weight.
The morphological changes during the
pre-fetal period are very extensive. The
occipital and the parietal protuberances of
the head decrease, the facial parts elongate, the neck and the extremities lengthen,
the umbilical hernia disappears, the abdominal wall strengthens, and the head is
inflexed away from the chest. The prefetal stage may be divided into two stages:
313
MULTIPLE PREGNANCY IN CATTLE
( a ) the early stage of development (30 to
45 days) when the embryo enlarges from
100 mg to 2 gm and ( b ) the late stage of
development (45 to 60 days) when the
embryo enlarges from 2 to 17 gm. Over-
crowding in utero did not seem to affect
the size of the embryo in the pre-fetal
stages; the retarding effect was shown at
the early fetal stages. In superovulated
rabbits overcrowding in utero had no
TABLE 5
Effect of litter size on organ development in 60-day f e t u s e s
Singles
Measurements
Triplets
Twin
Range
Mean
Range
Mean
Range
Mean
Liver weight (gm)
0.74-0.98
0.86
0.55-0.79
0.67
0.63-0.82
0.71
Digestive tract weight (gm)
0.43-0.77
0.60
0.38-0.56
0.47
0.33-0.53
0.45
Adrenals and
kidney weight
*
95-148
(mg)
Lungs weight (gm)
0.42-0.74
97-178
Heart weight (mg)
% eviserated fetus weight
to fetal weight
-
66-106
113
0.58
0.27-0.44
137.5
76
100-119
-
91
0.36
57-132
0.32-0.45
96
0.37
109.5
110-124
116.8
77
-
77
Skull length ( m m )
22-26
24
20-22
21
21-32
24
Tail length ( m m )
16-17
17
14-20
17
16-20
17
1
Both right and left.
Singles
Trip Ie t s
Twins
20
-
15
E
0,
z
L
10
01
r
r
0
f
5
Fetus
w Membranes
0
Fluids
\ 400
c
c
0
0)
0
Cr 200
r
0
f
Fig. 6 Effect of litter size on components of conceptus. Note the relative effect of overcrowding in utero on weight of fetus and placenta at 60 and 90 days of gestation.
314
E. S . E. HAFEZ A N D E . RAJAKOSKI
B
A
1
I
I
I
I
I
,
of the placenta before it shows its retarding effect on the size of the fetus.
From 60 to 90 days of single pregnancy
there was no evidence of differential growth
in the internal organs: i.e. no organs grew
faster than others. There is no data to illustrate the effect of litter size on differential
growth at that stage of pregnancy. Further
research is needed to study the effects of
litter size on the prenatal development of
different organs. The differential growth
rate throughout prenatal development has
been studied in sheep, by Wallace ('48),
who found that organs such as kidney,
liver, lungs, bladder and brain make a
larger proportion of their fetal growth
I
1
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I
!~=;d \
I
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'
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II
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1
I
Chori onic
----- A l la n t o i c
Fig. 7 Diagram showing patterns of placentation in multiple bovine pregnancy at 30 days.
A. Well developed necrotic tips and no attachment between adjacent allantochorions.
B. Partial attachment of adjacent chorions but
the allantoida not attached.
C . Complete attachment of allantoida and
anastomosis of the adjacent vascular supplies.
was affected. It is known that the sex differentiation of the embryonic gonads starts
at 45 days and is well defined histologically
at 60 days, Meanwhile, there were no significant differences in the weight or dimenOf Ossified bones in both
90-day fetuses.
Of
TABLE 6
Development of ossification centers in 60-day-old fetuses (measurements i n rnm):'
Measurements
Mandible
Scapula
10th Rib
Ilium
Femur
Tibia
Fibula
Metatarsus
Humerus
Radius
Ulna
Metacarpus
Eye ball
Triplets
Twins
Singles
Range
Mean
11.8 -13.0
4.25- 5.16
7.04- 8.43
1.78- 2.59
2.54- 3.03
2.88- 3.54
2.34- 2.91
1.30- 1.79
2.78- 3.43
2.84- 3.76
3.37- 3.85
1.50- 1.92
4.27- 5.11
12.2
4.47
7.95
2.07
2.78
3.15
2.55
1.54
3.15
3.29
3.57
1.70
4.65
Range
Mean
11.9
11.0 -12.5
3.89
3.58- 4.32
6.63
5.52- 8.15
1.70
1.27- 2.08
2.47
2.05- 2.90
2.67
2.19- 3.38
2.15
1.67- 2.86
1.05
0.64- 1.42
2.74
2.39- 3.13
2.84
2.47- 3.35
3.18
2.75- 3.70
1.27
1.02- 1.55
4.53
4.29- 4.76
Range
Mean
11.0 -12.9
3.70- 4.39
6.30- 8.50
1.35- 2.25
2.29- 2.96
2.46- 3.15
1.94- 3.33
0.87- 1.58
2.61- 3.24
2.65- 3.15
2.90- 3.43
1.05- 1.69
3.91- 5.09
12.3
4.02
7.34
1.79
2.62
2.84
2.41
1.30
2.98
2.97
3.25
1.42
4.48
Effect of
multiple
pregnancy
1
0.81
11.41
12.20
15.46
8.27
12.38
10.59
23.38
9.21
11.55
9.80
20.59
3.01
3 Difference between measuremeiits of single versus multiple fetuses as a percentage of measurements of
single fetus.
MULTIPLE PREGNANCY IN CATTLE
315
TWINS
TRIPLETS
I
QUADRUPLETS
Fig. 8 Diagram showing degree of attachment between adjacent allantochorions during multiple
pregnancy.
A. No attachment between allantoida.
B,C. Partial attachment of allantoida.
D. Complete attachment of allantoida i n both horns.
E,G,H. Envagination of allantoida in one uterine horn.
F. Envagination of allantoida in both uterine horns.
1,J. Complete attachment of allantoida i n one uterine horn.
Fig. 9 Ossification centers in 60- and 90-day fetuses. Note the proportional increase
during that stage of fetal development.
316
E. S . E. HAFEZ AND E. RAJAKOSKI
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