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.