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.
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.