Priorities For The Future

Because peak urinary E1C values range from ~100 to more than 800 ng mg_1 Cr before ovulation (Czekala et al., 2003; see also Chapter 8) and vary significantly among and within individual giant pandas, it is

Figure 9.6. Relative proportions of vaginal cell types for SB 371 during a normal oestrus in 1999 that included three artificial inseminations (arrows labelled AI) followed by a pregnancy and birth of a living young. Chromic shifts are also indicated by arrows (1 and 2), including two false second shifts (labelled 2 false) before the actual shift. Based on the actual second chromic shift, ovulation was predicted for 9 April. •, basophilic; x, acidophilic; o, kerantinised; —, superficial.

Figure 9.6. Relative proportions of vaginal cell types for SB 371 during a normal oestrus in 1999 that included three artificial inseminations (arrows labelled AI) followed by a pregnancy and birth of a living young. Chromic shifts are also indicated by arrows (1 and 2), including two false second shifts (labelled 2 false) before the actual shift. Based on the actual second chromic shift, ovulation was predicted for 9 April. •, basophilic; x, acidophilic; o, kerantinised; —, superficial.

impossible to predict the onset of the E1C fall that is indicative of ovulation. Chromic shifts in vaginal cells represent a rapid, inexpensive and dependable reflection of oestrogen and, thus, ovarian status. Furthermore, the consistent timing of the second chromic shift is predictive of the E1C fall. As emphasised repeatedly throughout this book, the successful breeding and management of the giant panda depend on

Figure 9.7. Relative proportions of vaginal cell types for SB 291 during an abnormal oestrus in 2002. The first chromic shift is indicated by arrow 1, but the second shift failed to occur. This female was not artificially inseminated. •, basophilic; x, acidophilic; o, kerantinised; —, superficial.

Date of February/March 2002

Figure 9.7. Relative proportions of vaginal cell types for SB 291 during an abnormal oestrus in 2002. The first chromic shift is indicated by arrow 1, but the second shift failed to occur. This female was not artificially inseminated. •, basophilic; x, acidophilic; o, kerantinised; —, superficial.

integrating disciplines and techniques. Vaginal cytology is now a proven tool to be added to intensive management strategies and is especially useful in the peri-oestrual interval.

Despite its effectiveness, vaginal cytology has not become a routine technique in most holding facilities, probably because of the need for behavioural conditioning to permit easy, nonstressful collection of vaginal cells. Thus, one priority is to apply this tool to more pandas in more facilities, especially as behavioural conditioning is becoming more common (see Chapter 11). It would be especially interesting to evaluate cytological profiles in females with a history of infertility (particularly in parallel with urinary hormone monitoring and behavioural assessments). This may provide new insights into the aetiology of suboptimal oestrus and the occasional phenomenon of failed ovulation (see Chapter 8).

Due to the value of this technique as a management tool, it would also be useful to explore the precise mechanism that induces nucleated intermediate cells to shift from basophilic to acidophilic in the vaginal smear. No change in the rate or concentration of E1C appears to correlate with the shift. However, this first chromic shift (easily apparent with modified trichrome Papanicolaou staining) is a definitive precursor to peak oestrus and ovulation in this species. Occurring eight or nine days before ovulation, it is a reliable indicator of impending oestrous events, thereby allowing staff to mobilise resources for a host of events ranging from intensive behavioural monitoring to the need to collect more frequent urine samples for measuring the E1C profile. No giant panda oestrous cycle examined to date has failed to exhibit a first chromic shift.

When it is impossible to collect daily vaginal smears, the observance of a preponderance of acidophilic cells is a clear signal that the first shift has occurred. Occasionally, acidophilic cells outnumber basophilic cells for one to two days before falling again below a 50% threshold. These false first chromic shifts can be misleading when pandas are not swabbed daily, thus emphasising the need to develop animal handling methods and facilities that allow swabbing as frequently as possible. Swabbing less frequently than once a day can result in misinterpretation of transient changes in vaginal cells. However, daily sampling can virtually always identify an authentic chromic shift that is irreversible and reflective of a forthcoming oestrus and ovulation.

As circulating oestrogens increase near the time of ovulation, a second chromic shift is associated with keratinisation of acidophilic cells one day before the urinary oestrogen peak and two days before the fall in this hormone. Again, false shifts can occur, the best example in our experience being the single, conceptive oestrous cycle in SB 371, a female that exhibited two false, second chromic shifts (see Fig. 9.6). Although this uneven rise in keratinised cells altered the normal interval between the two chromic shifts, the temporal relationship between the second chromic shift and ovulation remained unchanged. Similar to the first chromic shift, there was no clear rate change or consistent threshold of E1C concentrations that correlated to the second chromic shift. To fully understand the value of vaginal cytology as an index of the physiological dynamics of ovarian activity in the giant panda, further basic studies would be worthwhile. For example, investigating other forms of oestrogens or seeking out alternative hormone ratios might be useful to understand the driving forces behind altered vaginal cytology, including the chromic shifts.

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