Evaluating Reproductive Success in the Giant Panda

The reproductive biology of the giant panda has been studied extensively during the last 20 years, yet the biology of this species is still perplexing. For example, it was believed the panda ovulated only once each year, yet now it is known that sometimes a second ovulation will occur in the fall. In addition, when a conception occurs it is believed the panda has an obligatory, variable delay of implantation or diapause, but it is not understood what triggers the implantation nor is it known exactly when implantation occurs.

A recent study by the Reproductive Physiology Division of CRES, in collaboration wtih the National Zoo and New York University, of relaxin as a potential indicator of pregnancy revealed the hormone's presence in the urine of the panda; however, evidence was not sufficient to use it as a predictive tool of impending birth. Earlier studies suggest pregnancy can be detected by a sharp increase in a progestin metabolite during a brief period of time, approximately 20 days prior to birth. However, this peak is often observed with no subsequent birth of cubs. This has led to the speculation that undetected miscarriages could occur. This hypothesis was confirmed with the 2003 pregnancy of Bai Yun, a giant panda at the San Diego Zoo, where by both thermography and ultrasound multiple fetuses were detected but only one birth occurred. The simple method of detection of blood in the urine by Hemistix was used to suggest that miscarriage had occured. Four pregnancy categories were evaluated. The results were striking. Those females categorized as not pregnant and those giving birth had low levels of blood in the urine, while those females designated as pregnant yet without delivery (suspect miscarriage events) had statistically more days with positive Hemistix readings. These are preliminary data since the numbers of events are limited, yet the results suggest a high incidence of miscarriage.

This small study requires additional research to understand its relevance and accuracy. Additional events need to be monitored and, more importantly, a coordinated study integrating thermography, ultrasound, and hormone analysis, together with assessment of blood in the urine, is needed to fully understand the frequency of miscarriage in the giant panda. If these studies are correct, many conceptions occur in the panda that fail. If this is true, then the cause of these miscarriages needs to be determined to increase the reproductive success of the giant panda.

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