If you are a man in China, aged between 20 and 45, the government has a message for you: For the sake of your country, please donate sperm.

China's sperm banks are facing severe shortages, for a variety of political and cultural reasons.

Comparatively few Chinese men offer to donate and a study found that almost half of those who do volunteer to do so are screened out.

Now that government policy allows more Chinese couples to have a second child, officials are concerned that the sperm shortages will get much worse - and they are doing everything they can to find new recruits.

On social media, young men are bombarded with endorsements from video-game characters and promises of cash (up to US$1,000 or S$1,300, in some cases) and, even better, a coveted rose-gold iPhone.

Some sperm banks have tried to appeal to feelings of patriotism, as China grapples with an ageing population and a diminishing workforce.

"Show your compassion," an article on a state-run news site urged men this year. "Help mitigate the country's ageing problem."

Still, it is a tough sell. For one thing, Chinese traditional medicine has long associated high levels of semen with vitality, making some men reluctant to give any away.

In addition, despite rising rates of infertility, many families are uncomfortable with using an unrelated man's sperm to father children, arguing that it goes against Confucian values.

Recent ads have tried to counter those deep-seated attitudes.

"Donating sperm and donating blood are the same thing," said one message from a Beijing sperm bank. "It's all about giving back to society."

NEW YORK TIMES

•With additional research from Beijing by Emily Feng