Think of farmers in this instance as refineries that use soybean feed to convert Piglettes into Pork-Pigs. Tariff relief on USA brand soybean feed means that Chinese Piglette refineries will probably demand more of the USA brand feed than before because of the now lower price relative to other feed brands. However, at the same time, the refineries are experiencing a shortage of Piglette to mix with the imported soybean feed due to ASF and so they simply have lower feed needs/demands than before. You could make it more complicated by adding nuance like whether this will drive an increase in demand for imported pork as well which could, over time, stimulate USA/Worldwide feed demand as non-Chinese Piglette refineries expand and compete to fill the heightened demand for foreign pork (assuming things play out this way) but the overall gist is simply that there's pressure in two directions but probably not equal pressure.