Er Shun the inseminated panda on pregnancy watch at Toronto Zoo

The Toronto Zoo says it's monitoring one of its giant pandas for signs of pregnancy following artificial insemination.

Er Shun, one of the pandas on loan to Canada from China, was artificially inseminated in April, but the zoo says pandas' long gestation period makes it hard to know if it worked.

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It says staff will only find out about 20 days before Er Shun is set to give birth, and they're preparing her for an ultrasound.

The zoo says pandas only have one chance per year when they can breed and the breeding window lasts just one to three days.

The male panda, Da Mao, is too young for breeding, so sperm was flown in from China for the procedure.

The pandas will be at the Toronto Zoo until 2018, when they'll move to the Calgary Zoo for another five years.