Farmers in Dongying, East China's Shandong province, are adding the harmful chemical clenbuterol to sheep feed to produce leaner meat, Chinese media reported.
The latest food safety scandal was revealed in Dongying's Yanwo township, a booming farming area home to more than 1,000 sheep breeders.
Chinese media has reported that the use of clenbuterol, which was previously known to be used to produce leaner pork, was rampant and breeders were adept at fooling tests for additives.
The Beijing News reported that one breeder, whose real name was not given, said that to avoid detection he stopped feeding his sheep clenbuterol days before he took them to market.
Inspectors were usually stationed at entrances to major markets and randomly checked animals for illegal additives.
The breeder boasted sheep that failed to pass testing would simply be sold to individual buyers outside the market.
A 27-year-old local told China Daily on Wednesday that for years residents had refused to eat local mutton because they knew it contained clenbuterol.
Records from the market indicate the slaughtered sheep are sold to buyers in 17 municipalities and provinces, including Beijing, Henan and Jiangsu.
Clenbuterol, known colloquially as "lean meat powder", speeds up muscle-building and fat-burning, resulting in leaner meat. It is banned in animal feed because it can cause headaches, dizziness and gastric irritation in humans.
Every 300 clenbuterol-fed sheep earned breeders up to 20,000 yuan ($3,140) in extra profit because the leaner meat can be sold for more, the Beijing News reported.
Breeders said they could easily buy the chemical at local stores for 550 yuan to 1,200 yuan for each pack.
An investigation into the breeders has been launched, said Ge Huaizhou, deputy chief of the animal husbandry bureau of Lijin county, which administers Yanwo township.
Bureau chief Gao Heling said that at least a dozen officials work at the livestock market at all times to ensure quality inspection was carried out.
He added the samples suspected of being tainted with clenbuterol were always delivered to the provincial animal husbandry bureau for further tests.
The provincial animal husbandry bureau refused to comment when China Daily contacted it on Wednesday.
In March, the provincial bureau warned breeders that using illegal additives such as clenbuterol could lead to criminal punishment.
Liang Haoyi, a senior researcher at the China Animal Agriculture Association, cast doubt on the efforts of officials. "The local officials always try to conceal their malpractice when such food safety issues are exposed because it is their dereliction that partly caused such problems."
On Wednesday, the State Council, China's Cabinet, urged local governments to put an end to the use of illegal additives in animal feed.
In August, there were reports breeders in Hebei's Changli and Lulong counties were feeding sheep with clenbuterol.
