Is Er Shun expecting?

One of the Toronto Zoo's giant pandas on loan from China underwent an artificial insemination procedure on Thursday.

"We're really, really excited," Toronto Zoo Curator of Mammals Maria Franke told CTV Toronto on Friday.

"We just spent an all-nighter basically making things happen."

Reproductive scientists have been monitoring the female bear since January, the zoo said in a statement Friday. Earlier this week, the panda showed signs of entering the breeding cycle when her estrogen levels went up and progesterone level decreased.

"As this critical period of estrus lasts for 24 to 72 hours and only occurs once a year, the Toronto Zoo team had to act quickly," the statement said.

Er Shun had a non-surgical procedure using sperm collected from Da Mao, the other panda visiting Toronto from China. Since coming to Canada, Da Mao has showed no interest in breeding.

"They're still not really jiving each other," Franke said. "We're seing some aggression on the female side."

A second procedure was performed the same day using frozen sperm from two giant pandas living in China.

Giant pandas have what is called "delayed implantation," Franke said. Their gestation period can last anywhere from 87 to 186 days from insemination. As a result, the zoo will not know whether she's expecting until approximately 20 days before she gives birth.

Staff have trained Er Shun to stay still during ultrasounds, and hope they will be able to see a fetus, the statement said.

"Toronto Zoo staff will continue to closely monitor her and watch for any unusual behaviour." Zoo officials said the success rate of the procedure is typically about 60 per cent.

The panda couple is on loan from China to Canada for 10 years, five of which will be spent in Toronto and five in Calgary. But any babies conceived will remain in Canada.

The mother and baby have to be together for two years before the baby can be weaned, so if Er Shun gives birth toward the end of the five years, her stay at the Toronto Zoo will be extended past 2018.

Er Shun was artificially inseminated in April 2014, but the attempt was unsuccessful.

"We're keeping our fingers crossed that this is the year, second time's the charm," Franke said.