After the pair had mated between January 16-19, an ultrasound test was conducted on Friday on four-year-old Lin Hui, but the result showed no sign of pregnancy.

Zoological officials and media members keenly observed the test as veterinarians looked for changes in uterus shape that would be visible 164 days after the mating if Lin Hui was pregnant.

Vet Kannika Nimtrakul said it was possible Lin Hui had a pseudo-pregnancy because she had shown many symptoms of pregnancy in April such as producing breast milk, seeking solitude and getting upset with Chuang Chuang's presence.

Pseudo-pregnancies were common in pandas, she said, and Lin Hui no longer had these symptoms.

Zoological Park Organisation director Sopon Damnui said Lin Hui was not pregnant because she was still too young and her current environment was not suitable.

Zoo director Thanapat Pongpamorn said the zoo would invest Bt15 million to create a better environment by separating the pandas for at least three months before the next mating season - March next year - because they were naturally supposed to live in solitude.

He urged visitors wishing to see them together to visit the zoo before October.

Chuang Chuang's sperm would also be kept for artificial insemination and Lin Hui's hormone level would be checked every day, he added.

Sopon said Thailand would bring the Lin Hui case to a meeting of international panda experts in Chiang Mai in November. The meeting, which will discuss increasing the world's panda population and insemination techniques, will be the first of its kind to be held outside China.

The Nation