Farmer Zhang Qiang considers his pigs not just livestock, but national treasures.

He is among a handful of Chinese breeders who still specialize in native species -in his case, Wulian black pigs. Most others have switched to imported breeds.

"Almost all pork on the market in China is from species that originated overseas," said 41-year-old Zhang, who has two farms in Shandong province's Wulian county.

Pigs brought in from abroad grow faster and have leaner meat, Zhang said. "But they just don't taste as good."

So three years ago, he began to buy up every Wulian black pig he could find.

"We covered thousands of kilometers and went to hundreds of remote villages in the mountains," he said. "After searching for six months we'd collected just 30 pigs."

Today Zhang has 150 sows and more than 1,300 hogs. They are all that remain of the Wulian black pig, which in the 1980s numbered 3 million, according to Shandong's Department of Agriculture.

The pig, distinctive for its short legs, short neck and bright hooves, was listed among the province's endangered species of poultry and livestock in April 2009.

China is the world's biggest pork producer. The country's production last year was 53.3 million metric tons, almost 50 percent of the global total.

But research has found that more Chinese native pigs are dying out.

Wang Linyun at Nanjing Agricultural University said native species account for just 5 to 10 percent of the 50 million or so sows in China, while other experts estimate that 31 species are on the verge of extinction.

A Ministry of Agriculture survey from 2004 to 2008 showed four breeds, including the Shenxian in Hebei province and the Xiangcheng in Henan province, have already disappeared.

To reverse the trend, the government has placed 34 species under State-level protection, which means they cannot be slaughtered.