Tyson Foods and Hormel Foods have had processing plants and cold storage facilities barred from exporting pork to China over the use of a feed additive that promotes lean muscle growth.

Beijing requires third-party verification US pork shipped to the country is free of the additive ractopamine. While most countries regulate the use of ractopamine by allowing residues within internationally accepted tolerance levels, China does not allow it at all.

According to the US Department of Agriculture, pork packing plants disallowed for export to China include Tyson's plants in Perry and Storm Lake in Iowa, as well as its facility in Logansport, Indiana. Hormel's plant in Fremont in Nebraska has also been affected.

Tyson did not comment when approached by just-food. A spokesperson for Hormel said the "situation will have minimal impact to our business".

A spokesperson for the US Meat Export Federation told just-food: "It is difficult to predict when these plants' eligibility for China will be restored. Sometimes plants are allowed back into the market after just a few weeks, but on occasion it can take longer".

He added it was also difficult to predict the impact this would have on the US pork industry.

"China's domestic pork industry is massive – representing about half the world's pork production and consumption. So even modest swings in China's domestic production can have a significant impact on its demand for imported pork – either positively or negatively – regardless of how many plants we have eligible to serve the market."