BEIJING -- Beijing's animal health watchdog agency prevented more than 15,000 swill-fed pigs from entering the market between June and August as part of a government campaign to curb the spread of illegal slaughterhouses.

The Beijing Animal Health Inspection Institute said Tuesday that it found 157 pig farms in Beijing's suburban districts of Tongzhou, Shunyi and Fangshan using a mixture of liquid and solid food scraps to feed their pigs.

"The swill has not been properly disposed of on these farms. Pigs eating the waste are likely to carry dangerous diseases, such as foot-and-mouth disease," said a spokesman from the institute.

He said the animal quarantine departments will kill and bury any infected pigs that are found during routine quarantine checks.

An official with the veterinary department of the Beijing Agricultural Bureau said the pig farms gather swill from hotels, restaurants and canteens to feed their pigs at a lower cost.

The Chinese Law on Animal Husbandry forbids farmers from using swill as pig feed. However, there are no laws or regulations to penalize people who break the rule.

Local- and provincial-level government authorities, including that of east China's Shandong Province, are deliberating imposing fines as high as 20,000 yuan ($3,108) on farmers who use swill to feed their pigs.