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Canine Pregnancy: Predicting Parturition and Timing Events of Gestation

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Introduction Many aspects of canine pregnancy are unique among veterinary domestic species. Therefore, an understanding of the time course and clinical correlates of ovulation, fertilization, embryo and fetal development, and pregnancy specific changes in maternal physiology is essential when providing clinical services such as breeding management and monitoring of pregnancy [1-4]. It is also important for decision-making in cases of pregnancy failure, elective caesarian section and dystocia. One important fact is that gestation length and events of gestation are very repeatable and predicable when viewed in relation to the time of ovulation or the preceding the luteinizing hormone (LH) surge (Table 1 and 2). That is true, despite the fact that the normal interval from breeding to whelping can range from 55 to 70 days.
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In: Recent Advances in Small Animal Reproduction, Concannon P.W., England E.and
Verstegen J. (Eds.)
Publisher: International Veterinary Information Service (www.ivis.org)
Canine Pregnancy: Predicting Parturition and Timing Events of Gestation
(9 May 2000)
P.W. Concannon
Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York,
USA.
Introduction
Many aspects of canine pregnancy are unique among veterinary domestic species. Therefore, an understanding
of the time course and clinical correlates of ovulation, fertilization, embryo and fetal development, and
pregnancy specific changes in maternal physiology is essential when providing clinical services such as
breeding management and monitoring of pregnancy [1-4]. It is also important for decision-making in cases of
pregnancy failure, elective caesarian section and dystocia. One important fact is that gestation length and
events of gestation are very repeatable and predicable when viewed in relation to the time of ovulation or the
preceding the luteinizing hormone (LH) surge (Table 1 and 2). That is true, despite the fact that the normal
interval from breeding to whelping can range from 55 to 70 days.
Fertilization and Gestation Length
The reason why gestation length in dogs is relatively consistent when measured from the day of ovulation but
highly variable when measured from the day of breeding is partly understood. In the vast majority of bitches
parturition occurs 64, 65 or 66 days after the ovulatory surge in LH [1]. The latter represents the acute release
of LH from the pituitary in late proestrus or early estrus. The LH surge triggers the event of ovulation. Since
the day of the LH surge can be measured or estimated with reasonable accuracy, timing events from that day,
and using it as the reference point (Day 0) can be helpful. A 64 - 66 day gestation length measured from the
LH surge to parturition is the same as a 62, 63 or 64 day interval between ovulation and parturition, since
ovulation has been estimated to occur 2 days after the surge in LH [4].
In contrast, using the day of mating as a reference point, as observed in cases of just a single mating or
insemination, parturition can occur as early as 56 days later and as late as 68 days later. Similarly, a large
variation in apparent gestation length can be encountered when counting from the first of multiple matings or
the last of multiple matings, the extremes encountered differing by 2 weeks. For instance, if a bitch is held for
an aggressive stud dog and forced to mate starting 3 - 5 days before the LH surge, the interval from first
mating to whelping may be as long as 69 - 70 days. And, in rare instances where a bitch is still fertile 9 or 10
days after the LH surge and is bred then, the interval from mating to whelping can be as short as 55 or 56
days.
Part of the explanation is that dog sperm may, in some instances, survive in the bitch's tract for up to 7 or even
9 days and still remain viable in terms of being able to achieve fertilization and result in pregnancy. It is
possible that in dogs as in other species, many sperm die or loose fertility after 1 or 2 days. However, the
number that retain fertility for 2 days is sufficiently high in dogs that fertility and fecundity are not affected by
matings on the day of the LH surge, 2 days before ovulation. Thus, in such pregnancies, the sperm survived 2
days before potentially penetrating the oocyte, and the chromatin had to survive another 2 to 3 days to
function as a male pronucleus which fuses with the female pronucleus to form the 1-cell zygote. Fertility
declines with matings earlier than the day of the LH surge (i.e. mating 3 or more days before ovulation).
However, litters have occasionally been obtained from forced matings, matings by aggressive males, and
artificial inseminations of fresh semen as early as 3 - 5 days before the LH surge. Sperm deposition in such
cases was 5 to 7 days before ovulation and at least 7 to 9 days before oocyte maturation. Another part of the
explanation for the large variation encountered in apparent gestation lengths lies with the timing of egg
maturation in this species. In dogs (and foxes), unlike most other species, the eggs are still immature when
they are ovulated (i.e., they are still primary oocytes) and they do not complete meiosis and become secondary
(mature) oocytes until probably 2.5 to 3 days after ovulation. An egg must be a mature, secondary oocyte
containing a "female" pronucleus before the "male" pronucleus of a sperm can fuse with it to complete the
process of fertilization by forming the nucleus of the new one-cell embryo. In early-mated bitches, a sperm
probably penetrates each egg shortly after it is ovulated, but the male pronucleus once formed has to wait for
the egg to mature. In late-bred bitches, the female pronucleus of the matured egg is ready to fuse with the
pronucleus of a sperm that subsequently penetrates as soon as the male-pronucleus is formed.
The interval of nearly 3 days required for oocyte maturation after ovulation has been estimated in at least two
ways. One is based on estimating how long after ovulation that matings from different males can still result in
pups with different sires. Another is estimation of the time after ovulation at which mating with short-lived
frozen-thawed sperm results in pregnancies. Because of this phenomenon of "delayed" oocyte maturation,
bitches can readily give birth to litters with multiple sires when there are matings by different males before
ovulation.
Timing of Fertilization, Fertility and Fecundity
Thus, it appears that fertilization to the point of nuclear fusion can be accomplished no earlier than about 3
days after ovulation (and, thus, 5 days after the LH surge). Following maturation of the egg to
secondary-oocyte status, the fertile life span of an unfertilized egg may be only 1 or 2 days in some instances,
since fertility declines if matings are delayed until 4 and 5 days after ovulation (i.e., 6 and 7 days after the LH
surge). That is, both litter size and pregnancy rate decline when mating occurs more than 2 days after the
maturation of the oocyte. Thus, with a narrow 2-day window for optimal fertilization to occur, it is reasonable
that gestation length is consistent when measured relative to the day of the LH surge, or to the day of
ovulation. However, some bitches may have one or more fertile oocytes survive to as late as 7 or even 8 days
after ovulation which corresponds to 9 or 10 days after the LH surge. While fertility is typically low with
matings this late, when pregnancy does occur the gestation length is usually the same that as in other bitches,
i.e., with parturition occurring at 64 - 66 days after the LH surge (and 62 - 64 days after ovulation). The above
scenario is the basis of well documented cases of bitches with exceptionally short apparent gestation lengths,
giving birth to litters as "early" as 55 to 56 days after breeding. Why true gestation length is not always
obviously longer in these "late-bred" bitches is not clear, but there are two likely reasons. First, there is as yet
unpublished evidence that eggs fertilized 2 days after maturation divide slightly faster than eggs penetrated by
sperm before maturation. (Tsutsui, 1999, personal communication) Second, it is likely that the timing of
implantation is in part related to a sequence of events regulated by the timing of the changes in serum
concentrations of estrogen and progesterone. These do not differ with the time of mating or fertilization or
early embryo cleavage rate. It is likely then that there is a very narrow window of time in whh the uterus is
receptive for implantation. Implantation is estimated to occur at Day 22 - 23 after the LH surge [6]. In some
instances of a very late mating, there are anecdotal reports that, because of the resulting small litter size, the
fetal signal for parturition is weak, and parturition may be delayed for 1 - 2 days, with an apparent increase in
gestation length. However, documented evidence for this has not been published.
It is clinically useful to consider that gestation length in bitches is in most cases 64 - 66 days, when measured
as the interval from LH surge to parturition. However, it is important to realize that intervals of 63 and 67 days
have been seen in some normal, uncomplicated pregnancies and should not be considered out of the ordinary.
Furthermore, there can be error of up to 1 days in estimating the day of the LH surge. Nevertheless, estimating
the day of whelping as 65 days after the estimated day of the LH surge can be helpful to dog owners and aid in
scheduling whelping management services. Timing the major event of pregnancy from the estimated day of
the LH surge can also aid in pregnancy testing and pregnancy management services (Tables 1 and 2).
Table 1. Events and clinical correlates of canine pregnancy through the time of implantation
and pregnancy detection, aligned to days from pre ovulatory LH surge.
Days Events and changes in parameters
-25 to -3 Onset of proestrus (heat) - average Day -9
-3 to + 6 Onset of estrus behavior - average Day 0 to 1
-3 to +8 First acceptance of intromission and mating - average Day 1
-3 First day a single mating has significant fertility
0Pre ovulatory LH surge - time of major increase in serum LH
0Increase in progesterone from levels of 0.3 - 08 ng to levels of 0.9 to 3.0 ng/ml
0Onset of peak fertility for single matings by high-fertility studs
2Ovulation at 38 - 58 h after LH surge
3Primary oocyte(s) in oviduct. Potential penetration by sperm
4Oocytes presumably still without polar body or female pronucleus
5Maturation of oocytes in distal oviduct.. Fertilization completed if already bred
6Bred: 1-2 cell embryo. Non-bred: mature oocytes still fertile
7Bred: 2 cell embryo. Non-bred: viability of some oocytes declines or lost
8Bred: 4 cell embryo. Non-bred: late mating results in small or no litter
9Bred early: 4-8 cell embryo. Bred later: 4-8 cell embryo. Mating rarely fertile
10 Oviductal embryos: 8-16 cells
11 Oviductal embryos: 16 -32 cell morulae
12 Morulae inside zona pellucida found in uterine horns
13 Intra-uterine migration of blastocysts between horns
14 Migration within uterus continues
15 Ultrasound (U/S) does not detect any difference due to pregnancy
16 Enlargement of embryos and thinning of zona pellucida
17 Blastocyst enlargement continues. Migration stops
18 Zona enclosed blastocyst in > 1 mm diameter uterine vesicle. U/S detectable
19 Uterine vesicle visible on U/S. Embryo + zona pellucida. Mucoid coat
20 Embryo expansion in >2 mm x 3-6 mm uterine vesicle. Zona absent. Thin coat
21 Blastocysts touch, but are still unattached to, endometrium. Cannot be flushed
22 Uterine swellings grossly visible by d 21-23. Embryo attached. Invasion begins
23 Placental trophectoderm invasion of endometrium continues. U/S detects embryo.
24 Heart beats may be visible on U/S. Palpable 1 cm uterine swellings
25 U/S detection of heart beat
26 Rises in serum relaxin and acute phase proteins (fibrinogen) in some bitches
28 U/S detects zonary placental mass. Relaxin typically detectable
Table 2. Events and clinical correlates of canine pregnancy from implantation to parturition,
aligned to days from pre ovulatory LH surge.
Days Events and changes in parameters
22 Uterine swellings grossly visible by d 21-23. Embryo attached. Invasion begins
23 Placental trophectoderm invasion of endometrium continues. U/S detects embryo
24 Heart beats may be visible on U/S. Palpable 1 cm uterine swellings
25 U/S detection of heart beat with high-resolution equipment
26 Rises in serum relaxin and acute phase proteins (fibrinogen) in some bitches
28 U/S detects zonary placental mass. Relaxin typically detectable. Heart beats clear
30 Palpable, distinct 3 cm uterine swellings. Easy palpation. Prolactin increases
32 Increased prolactin levels detectable
34 Maternal anemia typically evident
36 Palpation yields less-distinct uterine masses. U/S detection of fetal limb buds
38 Embryo still shorter than placental girdle
42 Embryo starts to become longer than placental girdle
46 X-ray first detects skull and spine. Obvious increase in mammary development
50 Acute phase protein levels near peak
54 X-ray may detect limbs and pelvis
56 Teeth still not visible on X-ray
58 X-ray readily detects limbs and pelvis; possibly teeth
60 X-ray readily detects teeth by now or next day. Progesterone above 3 ng/ml
62 Progesterone begins to decline. Nesting, restlessness begins over next 2-4 days
63 Early parturition / short gestation, but not abnormal
64 Early parturition / normal gestation. Progesterone below 2 ng/ml 12-24 h pre-partum
65 Mean parturition date. Predicted whelping date
66 Late parturition / normal range
67 Very late parturition, but not abnormal absent signs of dystocia
68 Over-due if normal signs of nesting and whelping are absent
Major Events of Pregnancy
Some of the major events of pregnancy in the dog include the following, based on previous reviews and
reports [1-8]. Entry of embryo into uterus around Day 11; implantation around Day 22 - 23; secretion of
relaxin by the placenta by Day 24 - 28 and through term; increased secretion of prolactin by Day 30 and
through term and lactation; a physiological nornocyctic anemia evident by Day 30 or 35, and maximal (with
PCV reduced to 30 - 40%) at term; slightly increased secretion of progesterone from Day 30 through term,
probably due to the increase in prolactin secretion (since prolactin is luteotrophic); a simultaneous increase in
metabolism and fecal excretion of progesterone such that serum progesterone concentrations do not rise much
higher than in nonpregnant bitches; an acute pre-partum rise in prostaglandins to luteolytic concentrations and
a resulting rapid decline in progesterone concentrations during the 24 h pre-partum; a corresponding
p
re-partum behavior of nesting, digging, social withdrawal, defensiveness, and, also a corresponding drop in
rectal temperature of 1oC ; pre-partum and peri-partum discharge of normal green lochia; delivery (whelping)
of pup(s) with an average litter taking 4 to 24 h.
Timing Events of Pregnancy
The time-course of events of canine pregnancy that have been carefully studied all appear to be relatively
consistent among bitches and predictable when timed correctly. Timing can be accomplished based on the
following, listed in the presumed order of reliability:
(1) the day of the ovulatory LH surge determined by serum LH assay;
(2) the day of the LH surge as estimated by the detection of the concomitant rise in serum progesterone by
radioimmunoassay or sensitive ELISA;
(3) the day of ovulation as estimated by ultrasound;
(4) the day of LH surge and/or day of ovulation based on commercial ELISA progesterone assay;
(5) day of LH surge based on commercial urinary or serum LH assay;
(6) day of LH surge and/or ovulation based on the end-of-estrus (metestrus or diestrus) change in vaginal
cytology;
(7) day of ovulation based on changes in the vaginoscopic appearance of the vaginal mucosa; or,
(8) day of ovulation based on the timing of the pre-ovulatory softening of the vulva and perineum.
Time Course of Gestational Events and Clinical Landmarks
When the day of the preovulatory LH surge has been determined directly or based on progesterone
radioimmunoassay of the initial increase in progesterone in samples collected daily or more frequently, the
sequence of events that has been observed (or estimated) has typically been consistent across studies, and are
reviewed in tables 1 and 2. However there have been some variation and minor differences noted among
studies [typically 1 - 2 days] when studies have been done using a pre-defined, absolute concentration of
progesterone to estimate the time of ovulation. The day of parturition be predicted to be 65 + 1 days after the
estimated day of the preovulatory surge in LH with a reasonable degree of accuracy is effort has been placed
on accurate estimation of the day of the LH surge. The timing of other events are also predictable (Tables 1
and 2).
Impending Parturition and Elective Caesarian Sections
Pre-planned or elective c-sections can probably be performed safely after Day 63 after the LH surge.
However, there are no clinical research reports to this effect and special concern for support of the pups is
important. In other than brachycephalic breeds, waiting until Day 65 or 66 may result in spontaneous delivery
and obviate the need for c-section. In brachycephalic breeds initiation of surgery before natural labor may be
important, although there are no published data on the incidence of problems during natural delivery in these
breeds. Elective and emergency c-section is extremely safe as performed in the United States and Canada [5].
The pup mortality was the same as, or possibly less than, that observed with natural delivery, and bitch
mortality was 1%. The possible value of pre-surgical administration of dexamethasone has not been reported,
but there is anecdotal evidence of its successful use in some practices. The intention is apparently to mimic the
natural rise in corticosteroid that likely occurs at normal parturition. There is also anecdotal evidence that
incidence of prematurity, irregularities of fetal heart rates, and neonatal deaths can be reduced by first
confirming that the bitch is at term by assay of serum progesterone, but no reports have been published. It is
reasonable to suggest that at the time of surgery progesterone should be low, and preferably near or below 2
ng/ml, i.e. at levels expected within 24 h before natural labor. The same ELISA progesterone kits used to
monitor ovulation can be used in this regard.
Serum progesterone is at peak concentration between Days 15 and 30, and may reach peaks as high as 80
ng/ml (240 nmol/L ) or as low as 15 ng/ml (45 nmol/L ). In late gestation, Day 50 - 60, progesterone can be as
high as 15 ng/ml (45 nmol/l ) or as low as 3 ng/ml (9 nmol/L ). Progesterone typically declines from 4 - 5 ng
ml ( 12 - 15 nmol/L) to near or below 2 ng/ml (6 - 7 nmol/L) during the 24 h before the onset of labor. There
is a concurrent pre-partum decline in body temperature which is most readily observed with twice daily or
more frequent rectal temperature measurements started several days before parturition. Many practitioners
routinely have dog owners measure and record rectal temperatures 2 or 3 times a day starting 1 week before
predicted date of whelping.
Managing and Timing Pregnancies When Day of Ovulation is Unknown
The stage of pregnancy can be estimated based on several parameters. In recently bred bitches a vaginal smear
can determine if the transition from estrus to metestrus(diestrus) has occurred. This transition or shift in the
composition of the smear typically occurs 7 - 9 days after the LH surge, and thus about 57 days pre-partum. It
is not entirely accurate in that the metestrus or diestrus shift in the smear can occur as early a Day 6 and as late
as Day 11 (Concannon and Shille, unpublished observation). In early pregnancy, the size of uterine
enlargements palpable per abdomen can be helpful, being typically 1 cm at Day 22 - 24, and 3 cm at Day 32,
post LH surge. Ultrasound studies at know times relative to the LH surge have described several sonographic
landmarks of fetal development that can be used to estimate the stage of gestation when the day of the LH
surge is not known or accurately estimated. [7-10] Using ultrasound, the time of early detection of heart beat
depends on instrumentation, experience and preparation of the abdomen. However they are never delectable
before Day 23 and are likely to be delectable with any instrument by Day 28 - 30. The fetal length in relation
to the length of the placental girdle can be determined by ultrasound and results related to Day 40 - 42, when
the fetus crown-rump length becomes longer than the placental girdle. Details of other ultrasound criteria have
been reported [7-10], including first detection of the fetal limb buds at Day 33 - 35; eyes, kidney and liver at
Day 39 - 47; and intestine at Day 57 - 63. With radiography, the fetal skull is rarely visible before Day 45 and
is almost always visible by Day 47 - 49; pelvic bones are not visible before Day 53 and are usually easily seen
by Day 57; fetal teeth, not before Day 58 and usually by Day 63 [3].
References
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pseudopregnancy and pregnancy in dogs. In: Kirk RW, ed. Current Veterinary Therapy, Small Animal
Practice, Vol. X. Philadelphia:W. B. Saunders, 1989: 1269-1282.
2. Concannon PW, McCann JP and Temple M. Biology and endocrinology of ovulation, pregnancy and
parturition in the dog. In: P Concannon, D Morton, and B Weir, eds. Dog and Cat Reproduction,
Contraception and Artificial Insemination, Proceedings of 1st International Symposium on Canine and Feline
Reproduction. J. Reprod. Fert 1989; Suppl. 39:3-25.
3. Concannon P and Rendano V. Radiographic diagnosis of canine pregnancy: onset of fetal skeletal
radiopacity in relation to times of breeding, preovulatory luteinizing hormone release, and parturition. Am J
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4. Concannon P and Verstegen J. Pregnancy in Dogs and Cats. In: Knobil E and Neil JN, eds. Encyclopedia
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5. Moon PF, Erb HN, Ludders JW, Gleed RD, Pascoe PJ. Perioperative management and mortality rates of
dogs undergoing cesarean section in the United States and Canada. J Am Vet Med Assoc 1998;
213:365-369. - PubMed -
6. Thatcher M-JD, Shille V, Buhi WC, Alvarez IM, Concannon PW, Thibeault D, Cotton M. Canine
conceptus appearance and de novo protein synthesis in relation to the time of implantation. Theriogenology
1994; 41:1679-1692.
7. Yeager AE and Concannon PW. Association between the preovulatory luteinizing hormone surge and the
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8. Yeager AE, Mohammed HO, Meyers-Wallen VN, Vannerson L. and Concannon PW . Ultrasonographic
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All rights reserved. This document is available on-line at www.ivis.org. Document No. A1202.0500 .
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Serial ultrasonographic examinations were performed on 8 Beagle bitches from 20 to 60 days pregnant to determine time of first detection, appearance, and sizes of selected features of pregnancy. Gestation was timed from the day of the preovulatory luteinizing hormone surge. Findings related to gestational age were consistent among bitches. Gestational ages at earliest detection of the following features were: chorionic cavity at day 20; placental layers in the uterine wall at day 22 to 24; zonary placenta at day 27 to 30; embryo and heartbeat at day 23 to 25; yolk sac membrane at day 25 to 28; allantoic membrane at day 27 to 31; choroid plexus of the brain at day 31 to 35; fetal movement at day 34 to 36; skeleton at day 33 to 39; bladder and stomach at day 35 to 39; kidney at day 39 to 47; and liver hypoechoic, compared with lung, at day 38 to 42. Extra-fetal structures were measurable from day 20 or 22 through day 48. Chorionic cavity diameter increased from 0.2 +/- 0.0 cm to 3.3 +/- 0.2 cm, outer uterine diameter increased from 0.8 +/- 0.03 cm to 4.8 +/- 0.2 cm, length of chorionic cavity or zonary placenta increased from 0.3 +/- 0.03 cm to 4.9 +/- 0.05 cm, uterine wall thickness increased from 0.3 +/- 0.03 cm to 0.8 +/- 0.01 cm, and placental thickness increased from 0.1 +/- 0.0 cm to 0.5 +/- 0.05 cm. Chorionic cavity diameter, outer uterine diameter, and placental length each increased at a linear rate through day 37, after which time, each had a marked plateau in growth. Of the extra-fetal structures, chorionic cavity diameter was the most accurate for estimation of gestational age. All of the fetal structures studied increased at an increasing (second order) rate. Crown-rump length increased from 0.3 +/- 0.05 cm on day 24 to 9.2 +/- 0.2 cm on day 48. Body diameter increased from 0.2 +/- 0.03 cm on day 24 to 4.6 +/- 0.15 cm on day 60. Head diameter increased from 0.8 +/- 0.05 cm on day 34 to 2.7 +/- 0.04 cm on day 60. Of the fetal structures, head diameter was the most accurate for estimation of gestational age.
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There is considerable variation among bitches in commonly encountered intervals between cycles (5-12 months), durations of anoestrus (1-8 months), durations of follicular phase pro-oestrus (3-21 days) and periovulatory oestrous behavior (3-21 days), intervals from preovulatory LH surge to oestrus onset (-2 to 5 days), and intervals from fertile mating to parturition (57-68 days). The extent of variation within bitches ranges from slight to great. However, there appears to be very little variation in the intervals from LH surge to ovulation (2 days), to post-ovulatory oocyte maturation (approximately 4 days), to implantation (approximately 18 days), to selected developmental stages of pregnancy, or to parturition (64-66 days). There are no tests diagnostic of early pregnancy. The onset times of persistent pregnancy-specific changes have been estimated, including radio-opaque fetal details (Day 46), elevated blood prolactin values (Day 35), elevated blood relaxin values (Day 25), echogenic heart beats (Day 24) and embryonic vesicles (Day 19), and potentially palpable uterine enlargements (Day 21). As in humans, there is an anaemia of pregnancy involving a 30% reduction in haematocrit and an increased incidence of insulin resistance during the second half of gestation. Ovarian progesterone is required throughout pregnancy. LH and prolactin are luteotrophic in the pregnant bitch as well as during the 2-month luteal phase of the non-pregnant bitch. Parturition follows a luteolysis which occurs during an increase in prostaglandin F-2 alpha that begins 36 h pre partum. Factors regulating the duration of anoestrus are not known but termination of anoestrus is associated with increased pulsatile secretion of LH.
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The onset and progression of canine fetal skeletal radiopacity were studied in relation to the times of mating, the preovulatory peak in serum luteinizing hormone (LH) levels, and parturition for each of 6 pregnancies. Lateral radiographs were obtained at 2- to 3-day intervals 30 days after mating and at 1- to 2-day intervals during the period fetal skeletons became radiopaque. Radiographs were assessed as to whether fetal elements were absent, barely discernible, distinct, or obvious. Fetal skeletal elements were 1st detected 20 to 21 days before parturition (42 to 52 days after mating and 44 to 47 days after the LH peak). Radiographs of fetal skeletons, sufficiently distinct for an unequivocal diagnosis of pregnancy, were obtained 17 to 20 days before parturition (43 to 54 days after mating and 46 to 49 days after the LH peak).
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To describe dogs undergoing cesarean section in the United States and Canada, to determine perioperative management, and to calculate survival proportions. Multicenter prospective case series. 3,908 puppies from 808 dams. Survival rates immediately, 2 hours, and 7 days after delivery were 92, 87, and 80%, respectively, for puppies delivered by cesarean section (n = 3,410) and 86, 83, and 75%, respectively, for puppies born naturally (498). For 614 of 807 (76%) litters, all puppies delivered by cesarean section were born alive. Maternal mortality rate was 1% (n = 9). Of 776 surgeries, 453 (58%) were done on an emergency basis. The most common breeds of dogs that underwent emergency surgery were Bulldog, Labrador Retriever, Boxer, Corgis, and Chihuahua. The most common breeds of dogs that underwent elective surgery were Bulldog, Labrador Retriever, Mastiff, Golden Retriever, and Yorkshire Terrier. The most common methods of inducing and maintaining anesthesia were administration of isoflurane for induction and maintenance (n = 266; 34%) and administration of propofol for induction followed by administration of isoflurane for maintenance (237; 30%). Mortality rates of dams and puppies undergoing cesarean section in the United States and Canada are low. Knowledge of mortality rates should be useful to veterinarians when advising clients on the likelihood of puppy and dam survival associated with cesarean section.
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The size of the gestational sac and embryonic mass as well as the embryonic heartbeat were examined ultrasonographically from Day 16 to 25 of pregnancy in 15 beagle bitches, using a 7.5 MHz transducer. Results were more consistent when gestational age was based on the day of the preovulatory luteinizing hormone (LH) surge than on the day of first breeding. The gestational sac was first detected at 17 to 20 d after the LH surge, when it was 1 to 2 mm in diameter and 1 to 4 mm in length. The diameter and length of the gestational sac increased exponentially. At Day 25, the mean diameter was 8.2 +/- 0.3 mm (7 to 9 mm) and mean length was 20.3 +/- 1.1 mm (14 to 24 mm). Embryonic mass and heartbeat were first detected at 23 to 25 d after the LH surge. The embryonic heartbeat was detected on the day of or the day after detection of the embryonic mass, at which time the embryonic mass was 1 to 4 mm in length and was located at the periphery of the gestational sac.
Pregnancy in Dogs and Cats
  • P Concannon
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Concannon P and Verstegen J. Pregnancy in Dogs and Cats. In: Knobil E and Neil JN, eds. Encyclopedia of Reproduction, Vol. 3. New York: Academic Press, 1998. -Amazon
Hormonal and clinical correlates of ovarian cycles, ovulation, pseudopregnancy and pregnancy in dogs
  • P W Concannon
  • D H Lein
Concannon PW and Lein DH. Hormonal and clinical correlates of ovarian cycles, ovulation, pseudopregnancy and pregnancy in dogs. In: Kirk RW, ed. Current Veterinary Therapy, Small Animal Practice, Vol. X. Philadelphia:W. B. Saunders, 1989: 1269-1282.
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Yeager AE and Concannon PW. Ovaries. Uterus. In: Green RW, ed. Small Animal Ultrasound. Philadelphia: Lippincott Williams & Wilkins, 1995; 293-303. -Amazon -
Pregnancy in Dogs and Cats
  • Concannon P Verstegen
Concannon P and Verstegen J. Pregnancy in Dogs and Cats. In: Knobil E and Neil JN, eds. Encyclopedia of Reproduction, Vol. 3. New York: Academic Press, 1998. -Amazon -