No More Watching and Waiting for a 2004 Giant Panda Pregnancy
Following Mei Xiang's artificial insemination, Zoo scientists monitored her hormone levels to track pregnancy or pseudopregnancy.
September 15 Update
After Mei Xiang and Tian Tian did not breed naturally, Zoo researchers and animal-care staff vaginally inseminated Mei Xiang, but a cub this year was unlikely. more
On September 15, Zoo scientists confimed Mei Xiang had experienced a pseudopregnancy. more
Monitoring for Pregnancy or Pseudopregnancy
Zoo scientists monitored Mei's hormone levels to track the course of what turned out to be a pseudopregnancy, which she experienced last year. The chart below includes measures of both estrogen and progestins. As expected, urinary estrogens have declined to basal with a concomitant rise in urinary progestins. For the giant panda, an initial rise in excreted progestins occurs immediately after the peri-ovulatory estrogen peak. This initial post-ovulatory rise in urinary progestins signals that ovulation occurred.
An increase in progestins indicated that Mei entered into the final four-to-six-week period of her pseudopregnancy, which was more likely than a true pregnancy. During this period, the progesterone levels remained elevated before their eventual return to baseline.
September 15 Update: It looks like we'll need to hope for a pregnancy next year. Yesterday's urinary progestin concentrations were again baseline, and this was based on the assessment of two separate urine samples collected today. These results combined with ultrasonography confirm that Mei Xiang experienced a pseudopregnancy this year.
We continue to learn new information each year, and it is clear that the combination of urinary hormones, ultrasound, vaginal cytology, and behaviors will be extremely useful for assessing fertility and perhaps even diagnosing pregnancy in the future.
September 13 Update: Mei Xiang's urinary hormones declined to a level solidly within the range of baseline progestin concentrations. This year's profile tracks very closely to the data for 2003. In the absence of a birth, continued low levels of progestins excretion over the next day or so will lead us to the conclusion that a pseudopregnancy has occurred.
September 7 Update: Analysis of Mei Xiang's urinary progestins from September 5, 6, and 7 demonstrate a precipitous decline in hormone concentrations toward baseline. While these trends don't always follow straight lines, we certainly are rapidly approaching a point where urinary progestins will soon reach basal concentrations, probably within the next week, or even sooner.
Once again, using late July as our "inflection point" whereby the sustained "secondary rise" in urinary progestins began, we are now approximately 40 days into this interval, which we expect to last 40-50 days. We will increase our watch to 24 hours. Today's ultrasound looked very interesting but still not definitive. Mei Xiang has done some nest-building and cradling. She is very lethargic and thin.
September 2 Update: Urinary progestins continue to be quite elevated,although somewhat lower than last week. We still estimate that Mei Xiang is less than 40 days into this secondary rise phase (typically 40-50+ days), which is characterized by an accelerated production of progestins. Maternal behaviors are sometimes associated with declining progestins toward the end of a true—or pseudo—pregancy. It does not appear that a precipitous decline in progestins is imminent.
August 25 Update: Urinary progestins have increased dramatically to concentrations that exceed those excreted in past years. From these data we can begin to define the "inflection point"—representing the start of the secondary progestin rise—began on about July 28. Based on experience, we expect a 40- to 50-day duration for this secondary rise. We might expect to see concentrations decline to baseline in mid-September. Keep in mind that this is a "best-guess" estimate.
August 18 Update: Urinary progestins continue to rise demonstrating that we're now into the secondary rise phase.
August 12 Update: Mei Xiang is 105 days post-ovulation. Urinary progestins continue to be elevated, and we probably are at or near the beginning of the 40 to 50 day phase characterized by a secondary elevation in urinary progestins. Pseudopregnancies for the past two years lasted 147 (2003) and 160 (2002) days, respectively.
August 5 Update: It looks like we may be at the beginning of our secondary rise in progestins. The inflection point, or the point at which this secondary rise began, will become clearer as we accumulate more data in the next couple of weeks. Once the onset of the secondary rise is more clearly defined retrospectively, we then can count forward 40 to 50 days for an estimate of when to expect a decline in progestin excretion to baseline, which will signal the end to pseudopregnancy or birth.
July 29 Update: No substantive change over last week.
July 21 Update: No substantive change over last week; we are 83 days post-ovulation.
July 15 Update: Last week it looked as though the secondary rise in progestins was beginning, but this week's data don't support this. While the urinary progestins have been rising slightly, it doesn't appear that MX has yet entered into the 'secondary rise' phase, whereby we expect progestins excretion to be sustained in the range of 150-250 ng/mg Cr for 40 to 50 days.
July 8 Update: We are may be at the onset of the secondary rise in urinary progestins, but it will probably take another week or so to know for certain. There does, however, appear to be an increasing trend in progestin excretion beginning in late June. The secondary rise typically lasts 40 to 50 days.
Hormone Levels Leading up to Estrus
The chart below is a profile of Mei Xiang's estrogen levels from January 1 through May 2. The estrogen levels are plotted on the same scale (ng/mg Cr) that was used during Mei Xiang's estrous cycle last year. Peak estrogen concentration was about 140 ng/mg Cr in the sample collected in the morning of May 1. Later that same day, hormone concentrations fell precipitously to 80 ng/mg Cr in the sample collected at 4 p.m., and continued the downward trend towards baseline (30 ng/mg Cr) in the sample collected at 10 a.m. on May 2.
These data suggest that ovulation probably occurred in the 24 hours before the morning of May 2. From here on out we will focus on monitoring progesterone metabolites to assess pseudopregnancy.
Behavior Watch - Notes April 29
Mei Xiang continues to be restless, pacing, bathing, and scent marking at a high rate. However, her scent marking peaked on April 27 and has been decreasing since then. Last year she had a peak five days before estrus and then scent marking declined until two days after estrus when it increased again. When she is not pacing, she is up in her willow tree. Her repellant vocalizations have softened. On Thursday, April 28, she was observed backing into Tian on one occasion, but then rebuffed him for even considering it. He has attempted to align himself and drape himself over her opportunistically, and this behavior is also not received well. Her hormones continue to rise.
Behavior Watch - Notes on Week Six - April 26
Mei Xiang is beginning to display estrous behavior. She is spending most of her time in her tree. When Tian approaches she reproaches him. He managed one brief mount today before she repelled him. She is currently scent marking at twice the rate, 14 times per hour. Last year, at five days before estrus, she scent marked 7.3-7.6 times per hour. She is very restless and when not up the tree paces and scent marks. Her food intake has decreased. We have yet to see backwards walking, tail-up or lordosis and we have not heard any of the vocalizations associated with estrus (bleating and chirping).
Behavior Watch - Notes on Week Five - April 19
Behavior watches report no changes, which is in line with the hormone results.
Behavior Watch - Notes on Week Four - April 12
Mei Xiang's behavior remains the same with little to no scent marking. Tian Tian is showing signs of being in rut, demonstrating higher than usual levels of scent marking and locomotion.
Behavior Watch - Notes on Week Three - April 2
No significant changes in behavior were observed this week. The pandas continue to play somewhat more frequently than they do outside of the breeding season, and in some cases these play bouts are extended in length and vigor. Some observations of "play-mounts" have been recorded during these bouts. Mei Xiang was once observed backwards walking a very short distance to Tian Tian and appeared to sit in his lap. However, her general behavior to date cannot be described as proceptive or solicitous.
Behavior Watch - Notes on Week One - March 19
In the first week of our giant panda estrous watch, Mei Xiang showed few behavioral signs of estrus, such as a high rate of scent-marking and vocalizations. She is scent-marking from one to four times per hour, but this is only significant in that she doesn't scent mark much at other times of year. She has been investigating Tian Tian’s scent marks and the pair are engaging in lots of social play, but she is not yet making affiliative vocalizations.
Similarly, Tian Tian's behavior is little changed from that of the previous months, although his rate of scent-marking has increased over several months. At present, he is marking from zero to 25 times per hour. Activity and scent-marking frequency are expected to increase significantly when Tian Tian enters rut; his pirouetting frequency also is likely to increase.