Increasing breeding success in the giant panda requires a better understanding of its complex reproductive biology. We know that the female is typically mono-oestrus during a breeding season which occurs from February to May (within and outside China). Behavioural and physiological changes associated with pro-oestrus and oestrus last one to two weeks, during which the female exhibits proceptive behaviours, such as scent marking, to advertise her sexual receptivity (Lindburg et al, 2001). During the peri-ovulatory interval, receptive behaviours (e.g. tail-up lordotic posture) climax with copulation generally occurring over a one- to three-day interval. Birthing occurs from June to October with a gestation of 85 to 185 days (Zhu et al., 2001). This unusually wide gestation span is due to the phenomenon of delayed implantation, a varied interval before the conceptus implants in the uterus and begins foetal development. The driving force behind implantation in this species is unknown. The giant panda also experiences pseudopreg-nancy, whereby the female exhibits behavioural, physiological and hormonal changes similar to pregnancy.
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.
Behavioural and physiological cues associated with both pregnancy and pseudopregnancy include decreased appetite, nest-building and cradling behaviours, vulvar swelling and colouration, mammary gland enlargement and lethargy. Additionally, temporal and quantitative progesterone patterns (tracked by assessing urinary hormone byproducts and progestins) are indistinguishable between pregnancy and pseudopregnancy. Therefore, no definitive test currently exists for identifying pregnant from pseudopregnant giant pandas. However, endocrine and behavioural traits are useful for broadly estimating impending parturition and, in the absence of a birth, hormonal measures provide retrospective evidence of a presumptive pseudopregnancy. Although there is no doubt that the giant panda experiences pseudopreg-nancy, some presumed pseudopregnancies almost certainly represent failed pregnancies accompanied by undetected embryonic or foetal loss.
Endocrinology, particularly when combined with behavioural observations, has provided valuable insights into giant panda reproduction. Especially important has been the ability to measure hormones in animal excreta, historically urine and, more recently, faeces. These noninvasive measures provide animal care staff and researchers with a simple means of securing important physiological data without the stress associated with physical restraint or anaesthesia (generally required for collecting blood samples). In fact, the physiological stress resulting from such manipulations may obscure the ability to use blood samples to discern the normal underlying hormonal milieu. Additionally, evaluating steroid metabolites in urine or faeces represents a snapshot of hormonal activity while permitting long-term studies of reproductive patterns in individuals, populations or species, all without disturbing the animal (Monfort, 2003).
Urinary endocrine monitoring has been used for nearly 20 years in the giant panda. However, fewer than 25 females have been studied, and almost nothing is known about male reproductive endocrinology. For females, urinary oestrogens increase during the one- to two-week peri-oestrual interval when proceptive behaviours are prevalent and then decrease during oestrus; in fact, excreted oestrogen concentrations are rapidly declining at the time of mating (Bonney et al, 1982; Hodges et al., 1984; Chaudhuri et al., 1988; Monfort et al., 1989; McGee-han et al, 2002; Czekala et al, 2003). Endocrine databases for both sexes are now being rapidly expanded, largely because of international collaborations between Chinese breeding facilities and western zoos. The net effect has been more animals for study.
To provide a contemporary perspective of the unique reproductive endocrinology of the giant panda, this chapter reviews previous work as well as recent and novel research activities. Our focus is on the value of noninvasive endocrine monitoring (urinary and faecal), including radioimmunoassay (RIA) and enzyme immunoassay (EIA) techniques. Case studies of normal and abnormal endocrine cycles are presented, as well as endocrine responses to exogenous gonado-trophin treatments to stimulate ovarian activity. Data on androgen profiles in the male panda are offered for the first time, and preliminary evidence is presented on the potential for evaluating adrenal status (i.e. 'stress') in this species. We conclude by illustrating how this information can be used in an applied way to improve giant panda management.
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