A giant panda at the Memphis Zoo has miscarried, an ultrasound test discovered Wednesday.

Ya Ya, a 6-year-old panda on loan from China, was artificially inseminated in January.

The miscarriage was caused by her low level of the hormone progesterone, and she was not harmed by the pregnancy, zoo president Chuck Brady said shortly after the ultrasound was completed.

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Ya Ya was artificially inseminated after she and Le Le, her 8-year-old male companion, from China, failed to mate.

Brady said the zoo will attempt to mate the pandas again in January or February and will try artificial insemination again if that fails.

Pandas are notoriously poor breeders — one reason their species is endangered — and females have only three days a year in which they can conceive.

Three other U.S. zoos — San Diego, Washington and Atlanta — have giant pandas. T

he most recent panda cub born in the U.S. is Mei Lan, who was born in September at the Atlanta zoo.