Russia plans to stop accepting poultry from three plants in Mississippi, Louisiana and Georgia after officials said they found antibiotics and anti-parasitic drugs in chicken shipped from producers in those states.

Government officials in Russia — the largest U.S. export market for chicken — said they found traces of the drugs in meat from Sanderson Farms in Hammond, La.; Peco Foods in Canton, Miss.; and Tyson Foods in Cumming, Ga., USDA spokeswoman Bryn Burkard said Friday. Russia will stop accepting shipments from the plants March 27.

“We’re trying to find out why the Russians want to stop shipments from (the) Cumming plant, which is operating smoothly and continues to produce safe, high quality products,” Gary Mickelson, a spokesman at Tyson headquarters in Springdale, Ark., wrote in an e-mail.

“Since we have other U.S. poultry plants that are approved to ship to Russia, the suspension of the Cumming facility should not affect our overall international sales,” he wrote.

Spokesmen for the other two companies could not be reached Friday evening.

Russia imported more than 1.8 billion pounds of chicken from the United States last year, followed by mainland China at 733.9 million pounds, according to USDA’s economic research service.

“While Russia is an important leg quarter market for our company, our leg quarter sales to other regions of the world have been growing in recent years,” Mickelson wrote. “We are doing more business in places such as China, Africa and the Middle East.”

Burkard said the agency has asked Russia for more information. It was unclear what prompted the testing and why the drugs’ presence would have been unsatisfactory.

“Once we do have that, we will work with the establishments here and find whether antibiotics and anti-parasitics were in fact used, and then take appropriate action,” she said.