Pigs which died from disease or for other reasons were sent to Shanghai markets and restaurants over the past few years because farmers in a neighboring province were reluctant to pay for their proper disposal.
"You Shanghai residents just don't realize how many dead pigs you have eaten before," Xinhua news agency quoted a restaurant owner in Jiaxing as saying.
"In the past years, dead pigs were transported to Shanghai via mini-vans," the owner said.
"A van can carry seven to eight dead pigs and it was very easy to avoid supervision simply by installing wooden layers in the vans. Even if the van was caught by supervisors on the route, the driver would escape by leaving the van and all the pigs behind."
It was not until November last year, when 17 people in Jiaxing were punished for illegally trading in dead pigs that the business started to dry up or go underground, Xinhua said.
Pig farmers in the Zhejiang Province city said they had to pay 50 yuan (US$8) per carcass to "dead pig collectors" hired by the local government to ensure they were disposed of in an eco-friendly way.
An alternative was selling the pigs to illegal traders, who would pay about a yuan per 500 grams, farmers told Xinhua.
Others said they would simply leave the dead pigs by the roadside and the next morning they would be gone, probably taken away by illegal traders.
Official pig collector
Lu Gensong, an official dead pig collector hired by the local government, said he was paid 1,500 yuan a month for the job. It was a task made particularly easy from 2009 to 2012, when he said he didn't collect a single dead pig.
The illegal business hit the headlines last year when three people were sentenced to life in prison for processing more than 77,000 dead pigs and selling them for a total of 8.65 million yuan between January, 2009 and November, 2011. Another 14 people involved were fined or jailed.
That put paid to much of the trade but some farmers still dumped pigs by the roadside to be picked up rather than pay the government collectors.
Farmers in Jiaxing were reported to have raised a total of 7.34 million pigs last year. Of that number, more than 325,000 dead pigs were disposed of properly at 573 stations in the city.
According to the local government, death rates are around 10 percent which meant that many more dead pigs were unaccounted for.
Fewer dead pigs are being dumped now due to stricter supervision after more than 10,000 carcasses were fished out of the Huangpu River in Shanghai earlier this year.
Last month, a pig farm in Jiaxing confessed to dumping dead pigs in the river but didn't specify numbers, according to Xinhua.
But the Jiaxing city government insisted that not all the pigs had been dumped by its pig farmers.
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