The value and significance of vaginal cytology

barbara s. durrant, mary ann olson, autumn anderson, fernando gual-sil, desheng li, yan huang introduction

The giant panda is seasonally monoestrus, experiencing a single oestrus with spontaneous ovulation in the spring (Schaller et al, 1985). Although natural breeding produces the majority of cubs in captivity (Xie & Gipps, 2001), the number of sexually competent breeding males is insufficient to create or maintain a genetically diverse population (Hu, 1990; Xie & Gipps, 2001). Inclusion of males that are behaviourally incapable of mating, but that are genetically valuable, is possible through artificial insemination (AI) (see Chapter 20). Accurate monitoring of the oestrous cycle to pinpoint the time of ovulation is critical for timed matings and, especially, AI success.

The vaginal epithelium of many mammalian species is responsive to changes in circulating oestrogen concentrations. The value of vaginal cytology in monitoring the oestrous cycle of rodents (Zylicz et al, 1967; Parakkal, 1974) and domestic carnivores (Shutte, 1967; Mills et al., 1979) is widely recognised. In routine practice, evaluating vaginal cytology in these taxa involves quantifying proportions of mature exfoliated epithelial cells, also known as superficial, cornified or keratinised cells. Increasing proportions of mature cells are correlated with the pre-oestrual rise in oestrogen as well as oestrous behaviours.

Giant Pandas: Biology, Veterinary Medicine and Management, ed. David E. Wildt, Anju Zhang, Hemin Zhang, Donald L. Janssen and Susie Ellis. Published by Cambridge University Press. # Cambridge University Press 2006.

Despite the logistical difficulty of obtaining vaginal cells from most wildlife species, the oestrous cycles of several small carnivores (raccoon dog: Valtonen et al., 1977; river otter: Stenson, 1988; tayra: Poglayen-Neuwall et al, 1989; multiple ferret species: Mead et al, 1990; Williams et al., 1992; mink: Klotchkov et al., 1998; fox: Boue et al., 2000) have been described by analysing vaginal cytology. The few large carnivores studied to date include the sun bear (Onuma et al., 2002), American black bear (Reynolds & Beecham, 1980) and giant panda (Moore et al., 1984). These investigations have been based on only a single or a very few vaginal swabs per individual, which has yielded only modest information about cytological changes throughout the oestrous cycle. These studies also have relied on monochrome staining, which is effective for distinguishing nucleated cells from superficial (anucleated) cells but fails to identify changes in staining patterns over time. The application of a trichrome stain significantly enhances the ability to characterise vaginal cells that, in turn, provides more useful information on female reproductive status.

Among ursids, the sequential collection of vaginal cells from multiple individuals has been described only in the giant panda (Durrant et al., 2002). With behavioural conditioning, the captive giant panda can be trained to allow vaginal swabbing without chemical restraint or associated stress. This chapter reviews the value of this technology for monitoring female ovarian status and illustrates the positive correlation of oestrogen patterns with vaginal cell morphology. Therefore, this rapid, noninvasive technique is a useful tool for monitoring the dynamic events associated with oestrus and ovulation, thereby facilitating male introductions and/or AI.

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