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Pseudopregnancy

• Pseudopregnancy results when ovulation and corpora lutea formation occurs but pregnancy does not result.
• The corpora lutea produce progesterone which rises rapidly from basal concentrations (0.5 ng/ml) to 8.0 ng/ml 5 days after ovulation to a peak of 16 to 17 ng/ml 18 to 25 days post ovulation.
• Following the peak, progesterone concentrations decline to basal values at approximately 40 days post ovulation. The normal duration of pseudopregnancy has been observed to be from 35 to 40 days with an average of 36.5 days.
• The corpora lutea appear to have a preprogrammed finite lifespan in that they are not subject to regression from uterine sources of prostaglandins as is the case with cattle and horses.
• The corpora lutea also have been shown to be resistant to multiple luteolytic doses of prostaglandins through days 11 to 25 postovulation, indicating that it is clinically difficult to shorten the time interval from the onset of pseudopregnancy to the subsequent estrus.

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• This interestrus interval normally lasts 30 to 50 days and includes a luteal phase lasting around 35 days followed by a short 1 to 10 day anestrus phase. This anestrus phase may last several months if the queen is entering seasonal anestrus at the end of the pseudopregnant luteal period.
• It is rare for the queen to have overt signs of lactation (pseudogenetra) at the end of pseudopregnancy as seen in the bitch.

• Assuming successful induction of ovulation has occurred, fertilization can occur if viable sperm meet viable ova. Sperm cells undergo capacitation in vitro in approximately 1 hour.
• Fertilization probably occurs at the ampulla/isthmic junction, and the embryos move into the uterine lumen 4-5 days post coitus.
• Upon entry into the uterus, the embryos migrate for 6-8 days and then spread out so that each embryo has an equal share of the uterus.

• As the number of ovulations increases to greater than five, the percentage of embryos that implant at 12-13 days diminishes from 90% for 5 ovulations to around 53% for 9-11 ovulations. This overcrowding phenomenon results in an observed average litter size of 4-4.5 kittens, with the largest litters being 6.6 kittens from 8 ovulations.
• The fecundity of queens, therefore, appears limited by ovulation rates and uterine spacing.

Hormones of pregnancy

• In the pregnant queen, progesterone, secreted by the corpora lutea, rises rapidly after ovulation and peaks at a concentration of 30-40 ng/ml on day 21, which is very similar to that of the pseudopregnant queen. The concentration of progesterone then gradually falls to basal concentrations through the remainder of gestation.
• Unlike the pseudopregnant queen, the corpora lutea may not regress. In the pregnant queen the placenta produces the enzyme needed for progesterone production starting around days 28-32 of gestation, but the ovaries are still probably needed to maintain pregnancy to term. Needing the ovaries to term is different than what has been dogma for many years and still appears in most texts.
• Prolactin from the anterior pituitary increases at day 35 and peaks about day 50 of gestation. Prolactin appears to be needed for pregnancy maintenance. When a prolactin inhibitor, cabergoline, is administered after day 42, abortion results.
• Relaxin, from the fetal-placental unit, is detectable after 25 days of gestation, remains elevated from day 30 to term and declines abruptly at parturition. Laboratory tests using relaxin to diagnose pregnancy are being considered for the commercial market.
• During pregnancy, the queen has been reported to mate and ovulations at day 10-14 of pregnancy have been reported to result in a younger, secondary litter. This ovulation and secondary pregnancy is referred to as superfetation. However, reports on superfetation are mostly nonscientific and anecdotal so the phenomenon may not truly exist.

• Pregnancy diagnosis in the queen is easily determined by abdominal palpation. Discrete swellings in the uterus, which are the evenly spaced out fetal-placental units, can be palpated as early as day 16 post coitus in some queens until approximately day 30.
• After day 30, the fetal-placental units converge so that the discrete swellings become confluent. Radiography can be used to diagnose pregnancy after fetal mineralization occurs at about day 43 post coitus. At this stage, counting the number of conceptuses radiographically is easily performed.
• Ultrasound can be used to determine pregnancy as early as day 14-15 post coitus. The gestational sac appears as a round nonechogenic (black) structure located within a hyperechoic (white) uterus. Heartbeats are visible in the fetus starting around day 20. Although it is difficult to count the number of conceptuses accurately using ultrasound, the presence of fetal heartbeats gives an absolute indication of fetal life. The determination of fetal life is important in establishing when and if an early embryonic death occurs.

• Care of the pregnant queen should include adequate nutrition, adequate exercise, isolation from potentially infectious diseases and restraint from administration of vaccines or medications if at all possible.
• Queens eat more as gestation progresses. In one report individual queens ate an average of 178 gm of canned food during the first week of pregnancy, 267 gm during week 7 and 256 gm during week 8. Queens with larger litters tended to gain more weight than those with smaller litters, with an average gain of about 900 gm. The caloric requirement for pregnant queens is 100 kcal/kg of body weight. The ration must be balanced and specifically designed for cats.
• Vitamin A is essential in the queen's diet. Taurine deficiency may result in abortion or small kittens. Lack of adequate vitamin A can also cause early embryonic death and abortions.

• Gestation length in the cat is 63 to 66 days when measured from a fertile mating. Because kittens born before 60 days of gestation have little chance of survival, it is important that gestation progress to 63 days for maximum kitten viability.

• Prostaglandin F2alpha given at a dosage of 0.5 mg/kg IM daily for 2 days after day 40 of gestation can induce abortion within 8 to 48 hours after administration. Abortion of dead kittens or the birth of live, viable kittens is dependent upon the duration of gestation.