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National Zoo continues to check for signs of panda pregnancy

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By Michael E. Ruane
Washington Post Staff Writer
Thursday, April 1, 2010; 5:01 PM

The National Zoo said Thursday that the crucial period in Washington's annual giant panda pregnancy watch began last month, when experts detected the start of a rise in hormone levels in its adult female, Mei Xiang.

Once these levels start to rise, it is usually 40 to 60 days to the time when the panda gives birth or concludes what scientists call a false or pseudopregnancy, which is common in pandas and other bears.

Zoo reproduction expert Janine Brown said a panda's level of the hormone progesterone goes up when the bear first goes into heat, and then starts to go up a second time 70 to 100 days later. It is during the second rise that experts believe, if the panda is pregnant, the embryo implants in the uterus. Mei Xiang's secondary rise began around the middle of last month, Brown said.

"We're guessing the end of her breeding season is going to be around early May," she said.

At the end of that time, the panda's hormone level will drop back to baseline. "If we don't see a cub at that point, we just assume she was pseudopregnant," Brown said.

Mei Xiang, 11, was artificially inseminated Jan. 9 and 10 with semen from the zoo's male panda, Tian Tian, 12. The two adults are the parents of Tai Shan, the only giant panda to be born and survive at the zoo. Tai Shan, who was born in 2005, was sent to China on Feb. 4 to join a breeding program there.

Since the bear's artificial insemination, experts have been analyzing Mei Xiang's hormones via urine samples each week.

The zoo said it has tried to breed Mei Xiang for eight years. This year is perhaps the most important because the adult pandas are near the end of a 10-year loan from China.

"I can't tell you how wonderful it would be" to have a cub, said Brown, a research physiologist who heads the zoo's hormone lab. "It would be spectacular. . . . This would be a great time to have a baby."

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