The 55 percent fall was across both quality cuts and offal, where the United States has previously accounted for about a third of China's imports. U.S. offal shipments fell 58 percent to 177,041 tonnes, according to Reuters calculations based on data from the General Administration of Customs.

China is the world's main buyer of pigs feet, as well as other items like ears, elbows and innards, providing a source of revenue for U.S. processors which can barely sell such products at home.

Nine out of every 10 pigs' feet sold abroad by American processors in 2017 went to China, with total offal shipments to China generating about $874 million that year, according to industry and customs data.

China is the world's largest producer and consumer of pork, the country's most popular meat, and the top global importer, boosting its supplies with cheaper pork from abroad. Its total imports were worth about $4 billion in 2017.

However, U.S. pork sales to China fell after Beijing hit its pork products with two rounds of trade tariffs last year, taking total duties on frozen American pork to 62 percent.

China boosted offal supplies from some smaller suppliers, while imports from Brazil of higher value pork meat - known in the trade as muscle cuts - soared to 150,116 tonnes, the customs data showed, more than triple the prior year.

Germany and Spain were the top suppliers in this category, both shipping more than 200,000 tonnes, while imports from the U.S. fell 48 percent to 85,650 tonnes.

Total muscle cut imports for 2018 came to 1.19 million tonnes, a drop of 2 percent on the year before.

Analysts believe Chinese demand for pork imports could rise in the second half of 2019, as an epidemic of African swine fever spreading through Chinese farms looks set to sharply reduce the country's breeding herds.

The trade dispute has been a bonus for Brazil after major buyer Russia restricted pork shipments from the country in late 2017 amid a dispute over the presence of a banned feed additive.

Brazil is also benefiting from a much bigger share of China's soybean imports at the expense of the United States.

(Reporting by Dominique Patton, additional reporting by Beijing Newsroom, editing by Richard Pullin)