SHENYANG -- Doctors doing a special operation on a 21-year-old Manchurian tiger Monday confirmed that the tigress had a tumor in its abdomen, instead of original suspicions of the tiger being pregnant.

The event surprised doctors and forced crowds of reporters to swarm to the Guaipo Tiger Center in this capital city of northeast China's Liaoning Province to see "Mei Mei," which was expected to be the world's oldest mother tiger.

Manchurian tigers used to be found in northeast China and Russia's Siberia, living mainly on deer and wild boars.

Mei Mei, as old as a woman in her eighties, showed some early signs of pregnancy after mating with two male tigers many times in October last year, according to Ye Qingbai, manager of the tiger breeding center.

Experts estimated that the delivery will occur in early February, though to be pregnant was rare for such an old tiger.

A medical team from the No. 202 Hospital of the People's Liberation Army in Shenyang was well prepared to carry out an operation for the tigress during the last days before delivery.

But doctors was astonished to detect a tumor in Mei Mei's abdomen instead of an embryo Monday morning while taking a ultrasonic test after the tiger was anaesthetized.

The tumor, which is in the size of a human fist, and the swollen spleen were taken out at 12:30, and then sent to a local hospital for a pathological test.

The tigress seemed tired after the operation from the anesthesia.

"Because Manchurian tigers are ferocious, we can't check her without anesthetizing before&quobefore", said Zhao Wei, chief of the No. 202 Hospital. The life-span of Manchurian tiger is about 25 years. The world' s oldest mother tiger was reported as having cubs at the age of 16.

Mei Mei, considered to be a heroic mother, has given birth to a total of 15 cubs, and all of them survived. The last time she delivered baby
tigers was eight years ago.

Mei Mei has been fed with seven kilograms of fine beef during each meal, along with eggs, milk powders and calcium tablets in the recent three months.

Monitoring systems were equipped in Mei Mei's hut for round-the- clock supervision during her "pregnancy" and zoo keepers also regularly disinfected her room everyday for hygiene reasons.

Manchurian tigers are under state-level protection in China. They are among the top 10 most endangered species in the world, with about 300 remaining in the wild.

China has issued laws and regulations to protect endangered animals. A breeding center for feline animals was built in 1986 in Heilongjiang Province, northeast China, for the study of artificial breeding methods.

So far more than 100 Manchurian tigers have been bred there. Beginning from the year 2010, artificially bred Manchurian tigers being tamed for life in the wild are expected be released to their natural habitat in heavily forested mountain areas in the province, according to conservationists.