In this capital city of southwest China's Sichuan Province, some people were busy preparing a special kind of food for rats Saturday, by mixing peanuts with fluid that looks like egg white.

The fluid is nothing but a kind of contraceptive for rats, said Ye Qinglin, a scientist with the city's disease control center. Male rats will lose their capability to reproduce within two months after eating the contraceptive, Ye noted.

The rat-use contraceptive has passed official appraisal, and it will be produced in batches this March.

Traditionally, people kill rats with raticides, but the newly-developed contraceptive is aimed at reducing the numbers of the animal, said Zhao Erbi, a member of the Chinese Academy of Sciences, who attended the appraisal.

Similar to monkeys, rats are polygamous. One male rat has a group of female partners. The contraceptive kills the sperm of the male rat, but it does not reduce its sexual ability.

Jiang Guangzao, an expert with the Sichuan Provincial Institute of Plant Protection, said that this is the most economical way to fight rats, and poses no harm to humans.

For years, scientists have suspected that rats have been becoming wary of traditional raticides.

The government ordered a halt to the production of rat-killing tetramine after a series of murders involving use of the poison.