Figure 1. Timeline of actions taken during the experiment and the scheduled sampling of index and sentinel animals. Index gilts were bled on days 0, 3, 7, 14, 30, 60, 90, 120, 150, and 180 postinfection. Sentinel gilts were bled on days 90, 105, 120, 135, 150, 165, and 180. All samples were tested by the polymerase chain reaction, virus isolation, and enzyme-linked immunosorbent assay.