- Sperm cells enter the oviducts within 25 seconds of breeding. They do however, need around 7 hours to capacitate, before they are actually ready to fertilize. Sperm cells can live up to 7 days within the bitch's uterus.
- Progesterone is produced by the corpora lutea on the ovaries. The corpora lutea are the only source of progesterone for the canine pregnancy.
- Therefore, the bitch needs ovaries for progesterone production and maintaining pregnancy.
- A minimum of 2 ng/ml is needed to keep the bitch pregnant. If progesterone falls below this concentration, then the pregnancy will be lost.
- Progesterone is overall higher in pregnancy than in diestrus, although the overlap in the concentrations is too great to use as pregnancy diagnosis.
- Progesterone, after rising throughout estrus, peaks at 35-40 ng/ml around 15-25 days of diestrus.
- Progesterone slowly declines during the last week of pregnancy (or 1 week prepartum). During the last week of pregnancy there is an abrupt decline in progesterone concentration.
- Prolactin is luteotrophic in the pregnant bitch. It is needed to maintain the corpora lutea (CLs), even though it is very low in the beginning of diestrus. The prolactin concentration is inversely related to the progesterone concentration. As progesterone falls, prolactin rises. Therefore, prolactin rises starting at midpregnancy. Prolactin is at a higher concentration in pregnant, than nonpregnant bitches and higher in overt pseudopregnancy than diestrus without overt pseudopregnancy.
- Dopamine is a prolactin antagonist
- Prolactin is detectable by day 20-30 of pregnancy and peaks around days 40-50 of pregnancy.
- Relaxin is a pregnancy specific hormone that comes from both the placenta and ovaries, however it is primarily of placental origin.
- The packed cell volume decreases during pregnancy because of hemodilution caused by an increase in plasma volume.
- The PCV is <40% at day 35 of pregnancy and drops to <35% at term.
Gestation length
- The bitch is considered to have a variable gestation length. This variability is mostly because of errors in counting when conception occurred.
- If breeding dates are used to measure gestation, then gestation can be as variable as 57-71 days. This is because estrus is 9 days long and breeding can take place during any day of estrus.
- The most accurate day to measure from is the day of ovulation. In fact, gestation lasts 63 days from ovulation. Ovulation is however, hard to determine in many cases.
- If the LH peak is known, gestation can be measured as lasting 65 days from the LH peak.
- Gestation can be accurately measured from the first day of cytologic diestrus. Up to 80% of bitches whelp 57 days from the first day of cytologic diestrus. If behavioral signs of the female rejecting the male are used to determine the first day of diestrus, then gestation will be more variable. This variability is can be 2-3 days different than the first day of cytologic diestrus.
- Work done at LSU to determine if litter size has an effect on gestation length.
- Compared to Labrador Retrievers, German Shepherd Dogs, Golden Retrievers and hounds were more likely to have a longer gestation duration; three, four and nearly eight times as likely, respectively.
- Bitches with litters of four or fewer pups are likely to have longer gestation durations than those with five or more pups.
Induction
- Induction of parturition has been hypothesized to be similar to that of the sheep. In sheep it is well established that a rise in fetal ACTH causes fetal to cortisol increase. The fetal cortisol increase causes placental prostaglandin release then causes placental metabolism of progesterone to change to estrogen.
- Prostaglandins are produced near term in the bitch and probably play a role in the induction of parturition.
Problem pregnancies
- Discharges prior to parturition or previous problem pregancies
- Monitor fetal heart rate (should be about 200 bpm)
- Check progesterone (> 2 ng/ml they are probably not going to whelp)
- Fetal monitoring using WhelpWise fetal monitoring system
- To stop abnormal uterine motility use terbutaline and start with 2.5 mg q 6-12 h po. - only use if monitored.
Overt pseudopregnancy or pseudocyesis or pseudogenetra
- Each time a bitch enters estrus she is designed to become pregnant, so she goes into a luteal 'pseudopregnancy ' every time she comes into estrus. For learning sake, assume the hormonal events of pregnancy and diestrus are the same, even though prolactin is lower in the non-pregnant bitch. Prolactin is higher in bitches that have overt psuedopregnancies as compared to those that have covert pseudopregnancies. Diestrus can be considered a covert pseudopregnancy. Overt psuedopregnancy, or pseudocyesis or pseudogenetra occur in some bitches.
- The signs of pseudogenetra (overt psuedopregnancy, or pseudocyesis) include physical signs such as mammary development and lactation; and psychological signs such as nesting, mothering, and adopting inanimate objects.
- Pseudogenetra occurs at the normal expected whelping time.
- The cause is the rapid decline in progesterone at the end of a normal diestrus, coupled with a rise in prolactin (prolactin has been shown to be greater in overtly pseudopregnant bitches than normal nonpregnant bitches).
- Other events that exacerbate the signs are self nursing by the bitch, massage of the mammary glands by the owner, hot packs of the mammary glands, and milking the glands out.
- Iatrogenic pseudogenetra can be caused by ovariohysterectomy in diestrus. This results in a similar progesterone decline as seen in the naturally occurring condition.
- Progesterone supplementation during a pseudogenetra will temporarily stop the signs, but the removal of the progesterone will result in a recrudescence of the signs.
- Parturition may have occurred somewhere, so it is best to have done a pregnancy diagnosis at an earlier time. Ultrasound of the uterus can help to determine if the uterus is enlarged and the bitch may be postpartum.
- Mastitis and neoplasia are possibilities. Ultrasound and radiographs can help rule these out.
- Benign mammary hypertrophy occurs mainly in cats.
- Not treating is best!!
- Remove all physical causes such as self nursing by the bitch, massage of the mammary glands by the owner, hot packs of the mammary glands, and milking the glands out.
- Non phenothiazine tranquilizers can be used to calm the bitch. Phenothiazine tranquilizers can cause more milk release because they are dopamine antagonists and dopamine is a prolactin antagonist, so it will result in more lactation.
- Mibolerone is an androgen and has been shown to improve 100% of the physical and 90% psychological signs when administered at 0.016mg/kg for 5 days. It 'cured' 47% of the physical and 77% of the psychological signs. It has become unavailable again the US (8/2004).
- Bromocriptine (Parlodel) is a dopamine agonist, so it will result in more dopamine, less prolactin, and less lactation. Even though the prolactin is low in these bitches, it seems to help. This may be because of the sensitivity to low concentrations of prolactin. The dose is 20 ug/kg for 8-10 days. Side effects include vomiting, but this is apparently not as severe as some of the earlier reports indicated.
- Cabergoline (Dostinex) is also a dopamine agonist. It has fewer side effects than bromocriptine. The dose is 5 ug/kg SID for 5-10 days.
- Metergoline is a serotonin inhibitor and also inhibits prolactin. The dose is 2 mg BID for 10 days. It may cause whining and aggression. It is not available in the US.
- Estrogen and testosterone have been recommended by some sources, but they are not advisable to use.
- Mastitis
- Mammary hypertrophy
- Owner irritation.
- The good news is ovulation occurred, the progesterone rise occurred, progesterone fall occurred... everything worked !!!
- There is no predisposition to pyometra resulting from pseudogenetra.
by Bruce E Eilts
