Abstract

Until captive and free-ranging populations of giant pandas (Ailuropoda melanoleuca) are self-sustaining through natural breeding, reliance on assisted reproduction will continue to grow. Although artificial insemination is frequently used in captive pandas, little is known about the reproductive physiology in this species.

In a 5-year study, a pair of giant pandas was reproductively monitored and three artificial inseminations were performed from 1997 to 1999. After the arrival of the wild-caught, 10-year-old female (SB #378) at the Berlin Zoo in 1995, non-invasive urinary hormone analysis was performed weekly. Estrogen and progesterone concentrations as well as the behavior of the female indicated no sexual activity during her first 2 years in Berlin. In February 1997, she was evaluated by transrectal ultrasonography which revealed a normally developed genital tract but both ovaries appeared inactive. Estrus induction protocols were developed using PMSG with or without FSH priming. After treatment the animal showed clear signs of estrus based on urinary estrogen and progesterone levels, but she did not exhibit sexual behavior. The female was inseminated with frozen (first artificial insemination) and fresh (second and third artificial insemination) semen from the male (SB #208) 5 days after PMSG administration. The disposable artificial insemination catheter (2 mm in external diameter, Cook Inc., Queensland, Australia) was first inserted into the external cervical os by endoscopic visualization and then further guided by ultrasound into the uterine body. One milliliter of diluted semen was deposited in the uterus. We achieved no full-term pregnancy in the female, however, there was an indication of an embryonic absorption after the first artificial insemination. We suspect a pituitary malfunction may be responsible for the female’s acyclicity and the embryonic resorption.

Semen was collected from the male by electrostimulation after sonographic evaluation of the accessory sex glands. Between February and May, seven very good quality ejaculates were obtained with 2.75–4.0 ml volume, 85–95% motility, and 63–85% membrane integrity. Semen was used immediately for artificial insemination of the female or was cryopreserved. Post-thaw motility of the best ejaculate fractions was 35–40%. In September 1999, only an aspermatic ejaculate could be collected, indicating seasonal changes of spermatogenesis in the giant panda. More experimental research is needed but is limited by the small number of individuals and the panda’s endangered status. It is imperative that carefully designed studies be carried out first on a more numerous, non-endangered species to avoid inadvertent mistreatment of pandas.

To improve the knowledge on the reproductive physiology of bears, we extended our study and performed comparative ultrasonographic and endocrinologic investigations¹ in various ursid species (15 Ursus arctos arctos, three U. maritimus, two U. americanus, five Tremarctos ornatus, one Melursus ursinus). The reproductive physiology of ursids is characterized by seasonality and a period of delayed implantation between mating in April/May and implantation in November. There is convincing evidence that progesterone is produced during this period and that progesterone concentrations increase towards the end of diapause.^2,4 Giant pandas are also believed to utilize delayed implantation.³ However, monitoring of embryonic and fetal development has not been described to date.

Present results suggest that the reproductive biology of the giant panda finds its closest counterpart in ursids in the spectacled bear. However, due to the endangered status and limited access to this species, the American black bear and the European brown bear are being considered as a model for reproductive studies in giant panda.

Literature Cited

1.  Göritz F, Hildebrandt TB, Jewgenow K, Wagner N, Hermes R, Strauss G, Meyer HHD. Transrectal ultrasonographic examination of the female urogenital tract in nonpregnant and pregnant captive bears (Ursidae). J Reprod Fert Suppl. 1997;51:303–312.

2.  Hellgren EC, Vaughan MR, Gwazdauskas FC, Williams B, Scanlon PF, Kirkpatrick RL. Endocrine and electrophoretic profiles during pregnancy and nonpregnancy in captive female black bears. Can J Zool. 1990;69:892–898.

3.  Hodges JK, Bevan DJ, Celma M, Hearn JP, Jones DM, Kleimann DJ, Moore HDM. Aspects of the reproductive endocrinology of the female giant panda with special reference to the detection of ovulation and pregnancy. J Zool. London. 1984;203:253–267.

4.  Tsubota T. Studies on reproductive physiology of Hokkaido brown bear, Ursus arctos yesoensis Japanes. J Anim Repro. 1990;36:1–10.