Published online by Cambridge University Press: 09 August 2009
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 pseudopregnancy, whereby the female exhibits behavioural, physiological and hormonal changes similar to pregnancy.
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 by-products and progestins) are indistinguishable between pregnancy and pseudopregnancy. Therefore, no definitive test currently exists for identifying pregnant from pseudopregnant giant pandas.