![]() Several endocrine differences have been reported for pregnant bitches when examined in comparison to nonpregnant bitches in the same stage of the ovarian cycle. An "in-clinic" canine serum relaxin ELISA assay is marketed for this. Serum relaxin assay after Day 30 is diagnostic. Biochemical pregnancy tests have included nonspecific assays of fibrinogen and of c-reactive protein, which are not specific. Fetal heart rate (average around 230 bpm) can be monitored readily by ultrasound, beginning at Day 28. Pregnancy can be diagnosed by manual palpation of discrete uterine enlargements between Day 20 and 35 by ultrasound after Day 25 and by radiography after Day 46. The marginal hematomas develop large pools of stagnant blood from which the extra-embryonic circulation absorbs metabolites and iron. The girdle of fetal trophoblast tissue develops marginal hematomas, while the chorioallantoic poles remain thin and transparent. The timing of the events of canine pregnancy are also reviewed in Concannon, 2001 (Placentation is endothelial-chorial, zonary and circumferential. As the placenta and embryo continue to grow, the embryo is shorter than the length of the placental band until Day 38-40 and is obviously longer than the placental girdle after Day 42. Using high-resolution (7 to 10 MHz) ultrasound, embryonic vesicles are first detectable at Day 18-20, embryonic masses at Day 21-23, fetal heart movement at Day 24-25, the zonary placenta at Day 28, and fetal body movement at Day 35. Available data suggests that blastocysts typically enter the uterus around Day 10-12, pre-implantation uterine swellings are grossly detectable around Day 18, trophoblast attachment occurs around Day 21, and implantation around Day 22. Implantation is apparently timed by maternal endocrine changes initiated around the time of ovulation. Gestation almost invariably lasts 64, 65 or 66 days after the LH surge (Day 0), whereas the interval to parturition following a single mating can range from 56 days (following a "late" mating) to 69 days (following an "early" mating). Implantation, Placentation and Timing of Pregnancy Events ![]() In some cases, matings as late as Day 9-10 have resulted in pregnancies lasting only 56-57 days after mating. Pregnancy rates and litter size decline progressively with matings after Day 6, due to oocytes degeneration and cervical closure. Having multiple sires for a single litter is not uncommon. Dog sperm may remain fertile in the female tract for up to 8 days and pregnancies have resulted from single matings at 5 days before ovulation. Lengthy fertile life spans of spermatozoa in the female tract and of mature oocytes in the oviducts in this species may explain the high fertility rates (>95%) often obtained in commercial dog breeding facilities. ![]() Following oocyte maturation, bitches remain fertile for 2-4 days, or longer. Oocytes are ovulated as immature primary oocytes, and become mature after a 2 or 3-day period in the oviducts (uterine tubes). Estrus behavior, and copulation, may begin as early as 5 days before ovulation or as late as 3 days after ovulation. Ovulation occurs spontaneously about 2-2.5 days after the preovulatory LH surge. ![]() Luteal function is terminated by an abrupt prepartum luteolysis. However, there are secondary increases in circulating progesterone beginning between Days 25-35, despite increased progesterone metabolism and fecal excretion, reflecting a pregnancy specific stimulation of progesterone production. The luteal phase of pregnancy involves an initial peak in progesterone around Day 15-25 and a subsequent slow decline, with concentrations comparable to those in non-pregnant cycles. Pregnancy length in dogs is remarkably consistent, being 64-66 days from the preovulatory LH surge to parturition in nearly all instances. ![]()
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