The Pallas' cats arrived from the San Diego Zoo last year and were implanted with embryos. The embryos were made with eggs taken from other cats in the Cincinnati Zoo that were inseminated with sperm drawn from wild cats in Mongolia.
But sonograms done by a medical team from the Cincinnati Zoo this week show the Erie cats aren't pregnant.
There are only 45 Pallas' cats in captivity in North American zoos.
Bill Swanson, director of the Cincinnati Zoo's center for Conservation and Research of Endangered Wildlife, says officials had hoped success with the procedure would lead to similar success with other animals.
