Tangrenshen Group has found feed it produced contaminated with African swine fever, raising fears of its spread further across China.
It is the first report of contaminated feed in an industry squeezed by tight margins.
In a statement to the Shenzhen Stock Exchange, the company said the disease was found in feed samples provided by its 51 percent-owned subsidiary, Bili Meiyingwei Nutrition Feedstuff.
The discovery occurred during inspections after an outbreak of African swine fever on a farm in Qingyang county located in the eastern Chinese province of Anhui.
Tangrenshen said the origin of the disease remained unclear and the matter was still under investigation.
China has struggled to stem the rapid spread of African swine fever, which has now reached most of the country's pig-farming regions. The country produces almost 700 million pigs a year, or about half of the world's total.
