When China levied additional tariffs on pork from the United States last year, Zhu Mengzhou, a manager of an imported food distributor in Guangzhou, was one of many traders who stopped buying it. “Unless the tariffs are adjusted, the cost is too high for us,” Zhu said. Even as an outbreak of African swine fever threatens to decimate China’s most important meat market, Zhu cannot afford to resume US purchases due to two rounds of trade war tariffs which added a total of 50% to import duties. For some US pork products, Chinese buyers have to pay duties up to...