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Estradiol reaches peak levels of 50 to 100 pg/ml in late proestrus, one or two days before the LH surge. Circulating levels of estrogen metabolites have been reported as long as several weeks into pregnancy.
Progesterone levels remain between 0.5 - 1.0 ng/ml until the LH surge. The rise in progesterone level after that surge is variable in time and duration. Levels of progesterone may reach 15-85 ng/ml at 30 days post LH surge. Although progesterone levels in both pregnant and not pregnant bitches are high, the differential is not an accurate estimate of pregnancy. Progesterone is the only steriodal hormone required for pregnancy maintenance. There is not evidence that steriodogenesis occurs in the canine placenta. The corpora lutea produce all the progesterone needed to maintain the pregnancy. During the latter period of pregnancy the level of progesterone drops to 2-5 ng/ml. There is a drop in progesterone 24 hours before whelp to below 1 ng/ml.
Post implantation anemia characteristic of canine pregnancy is an accurate differential technique for distinguishing pregnancy from pseudopregnancy.
LH and FSH are most elevated during estrus. LH levels continue to support the production of progesterone by the corpura lutea during pregnancy. In late anestrus FSH and LH again interplay to create the onset of the next estrus.
Prolactin fluctuates during estrus and implantation. A surge occurs as progesterone decline in the 35-40 day of pregnancy. A ten-fold increase occur from that point until parturition. Following birth the levels decline to a steady level until lactation is complete.
Prostaglandins are luteolytic in the bitch and may be the major changes in uterine tone and myometrial activity in late pregnancy. PG2a is low during pregnancy while other products of arachidic acid, PGE2 and PGI are considerably elevated.
Fertilization is probably limited to 3-day period from days 4-7 (post LH surge) 2-5 days after ovulation. The embryos are present in the lumen until the 15-18 day. Distinct swellings of implantation sites become evident by day 18 during the formation of the embryonic primitive streak and the initial development of the placenta. Uterine swellings are lcm at day 20 and represent localized uterine edema, expansion of the embryonic membranes and early placental development. By day 30, uterine swellings are 3cm in diameter.
7.2.1 POSTIMPLANTATION EVENTS
Body weight gains during gestation range from 20-50% the average is 36%. Almost all the weight increase occurs in the latter half of pregnancy.
The maternal hematocrit slowly declines following implantation usually below 40% (PCV) by day 35 and below 35% (PCV) at day 40. There is an increase in hemoglobin and a decline in the sedimentation rate throughout pregnancy.
Immunosuppression during pregnancy is common. IgG levels below 500 mg / dl have been reported. A 30% decrease in serum creatinine also occurs.
Sensitivity to insulin, but not glucagon, means that in the pregnant female doses of insulin are much less effective at reducing the plasma glucose levels.
The caloric needs increase to 45gm of dry matter per kg body weight during the last half of pregnancy. Bitches maintained on 70% carbohydrate levels in the diet have healthier litters and less mortality.
Delivery of an average litter is usually rapid and complete within 4 hours. The delivery of the first pup nearly always occurs 64-66 days following the LH surge while it may range from 57-72 days from the first of multiple matings. Gestation may be longer in bitches bearing a single pup.
The major endocrine event is the rapid rise in estrogen in the peripheral blood which occurs 24-36 hours ahead of the event. It stays elevated until delivery is complete. The fall in progesterone is occurs gradually. It is usually below 1 ng/ml 9 hours before whelp. Plasma cortical levels fluctuate during the last week of gestation, but are remarkably elevated during the day of parturition.
The myometrial sensitivity to oxytocin levels occur during the decline in progesterone levels. Relaxing levels have not been measured.
Rectal temperature starts to fall about 1 degree C between 12-24 hours prior to the onset of parturition. The hypothermia is transient and temperature rises immediately after parturition and remains slightly above normal for as long a one week.
First stages of labor are associated with restlessness, seeking seclusion and decreased food intake. Mammary turgidity and secretion of milk may be obvious 1-2 days prepartum. Panting, scratching, chewing and nesting are noted 12-24 hours before delivery.
Stage II of labor the fetuses are delivered through the cervix and vagina. There is evidence to suggest the horns alternate in expulsion of fetuses. Intervals between delivery of individual pups may be 2-3 hours apart but intervals are usually shorter, 45 minutes to an hour.
The green discharge may precede birth of the first pup. The green color of the discharge results from the release of stagnant blood products, primarily uteroverdin of the marginal hematomas during placental dislocation. Normal post partum involution occurs within 8-12 hours post partum.
Ectopic pregnancy as been observed infrequently in the dog.
Prolonged gestation is usually an artifact due to the variability of mating period.
Spontaneous abortion and embryonic death have been documented with ultrasound to occur during the first half of pregnancy. Drugs like corticoids and chloramphenical will disrupt pregnancy. Infectious agents cause abortion, and or placental death. Escherichia coli. Brucella canis leptospira, Toxoplasma gondii, b hemolytic streptococcus, type G & D and campylobacter have been noted. Herpes virus and Mycoplasma/Ureaplasma are also noted.
Fetal anomalies and chromosomal aberrations are reported in people.
Uterine torsion has occasionally been reported.
Hypocalcemia usually occurs during peak postpartum lactation by may occur prepartum. Trembling, weakness may progress to convulsions at calcium concentration fall below 8mg/dl.
Hypoglycemia during pregnancy presents with very similar signs. Blood glucose levels may fall to 40mg/dl.
Dystocia may be caused by maternal or fetal factors. Common are, narrow birth canal, vaginal strictures, and primary inertia (failure to begin labor 24 hours after a drop in serum progesterone below lng/ml). Fetal causes include fetal monsters, large fetuses and fetal death.
Oxytocin is used to increase the strength of uterine contraction only. Failure to respond to 2 injections and a caesarean section should be performed.
MOTHER ------------------ > FETUS <--
-------> . . .
KIDNEY LIVER . LIVER KIDNEY .
. .
. .
. _ _ _ _ _
Metabolites ---------
Pyometra is a hormonally mediated diestral disorder resulting from bacterial and Mycoplasma interaction with an abnormal uterine endometrium that has undergone pathologic changes assumed to be caused by an exaggerated response to progesterone stimulation Progesterone promotes and supports endometrial growth and glandular secretion while suppressing myometrial activity, thus allowing accumulation of uterine glandular secretions. These secretions provide an excellent environment for bacterial and Mycoplasma growth. Bacterial growth is further enhanced by inhibition of the leukocyte response to infection in the progesterone-primed uterus.
A condition called endometrial hyperplasia usually precedes the development of pyometra. Continued hyperplasia following numerous estrus periods results in cyst formation. Mucus debris and the accumulation of a thin watery fluid is observed normally but may predispose to the cystic endometrial hyperplastic condition over time. Hydrometra or Mucometra are terms used to describe these conditions in the exaggerated form.
The most likely source of the bacteria and Mycoplasma is the vaginal flora. The potential of ascending through the relatively dilated cervix, into the uterus, occurs during proestrus and estrus. The vaginal culture provides excellent information on the predisposition to pyometra in the bitch. The culture should be done during the anestrus period to determine the resident microflora rather than to culture during estrus when opportunistic organisms in the vestibule may contaminate the culture.
Pyometra signs vary depending on the patency of the cervix. All mucopurulent and sanguineous discharges that occur after the end of the estrus period should be evaluated. The discharge of pyometra usually occurs 4-8 weeks post breeding. The following laboratory aids are needed to properly diagnose the disease:
Pyometra can be treated by surgical removal of the uterus and ovaries or by chemical emptying of the uterine infectious debris. Broad spectrum antibiotics and supportive therapy are continued in either case, 14 days.
