Female Giant Panda's Hormones on the Rise 4/27/2010

Scientists at the Smithsonian’s National Zoo detected a secondary rise in urinary progestagen levels in the Zoo’s female giant panda Mei Xiang (may-SHONG) March 30. This hormone rise indicates that it should be 40 to 50 days before Mei Xiang either gives birth to a cub or comes to the end of a pseudopregnancy, or false pregnancy, which is common in giant pandas.

“The hormonal dynamics of pregnant and pseudopregnant pandas are extremely similar,” said Janine Brown, reproductive biologist at the Zoo. “We study the hormone levels, work from past data and monitor her behavior closely, but all signs can indicate she is pregnant when she is not. So we remain hopeful, but cautious.”

Similar to last year’s unusually early estrus, Mei Xiang once again came into heat at the beginning of January, with Zoo scientists artificially inseminating her with semen from male giant panda Tian Tian (t-YEN t-YEN) Jan. 9 and Jan. 10. There is no conclusive study that indicates what causes panda ovulation, although scientists know that giant pandas mostly breed in late winter to early spring.

Since the artificial insemination, scientists have conducted weekly hormonal analyses on urine samples from Mei Xiang. Zoo veterinarians are also conducting weekly ultrasounds on her to monitor any changes in her reproductive tract and look for evidence of a fetus. So far, they have not seen an indication of one. Because panda fetuses do not start developing until the last weeks of a gestation period, Zoo veterinarians say they do not yet expect to see a fetus. They stress that it is still too early to determine if Mei Xiang is pregnant or experiencing a pseudopregnancy. In 2005, in the last weeks leading up to the birth of Mei Xiang’s only cub Tai Shan, she would not cooperate for her weekly ultrasounds, and it was not possible to definitively determine if she was pregnant.

This is the eighth year the Zoo has tried to breed the giant pandas. Mei Xiang gave birth to Tai Shan in 2005. Mei Xiang, 11 years old, and Tian Tian, 12 years old, are on loan from China through the end of 2010. They both live at the Fujifilm Giant Panda Habitat at the National Zoo.