Variation in mean rectal temperatures, scores for main clinical signs, and body weights in each infected group. (A) The average rectal temperature of the HP-PRRSV/PCV2 group (18–21 dpi) was significantly higher than that of the PCV2/HP-PRRSV sequentially infected group, the HP-PRRSV+PCV2 group, or the HP-PRRSV group. The temperatures of the uninfected control group and the PCV2 group were normal. (B) Variations in the mean clinical sign scores. The mean score is the sum of five individual scores, each ranging from 0 to 2, resulting in a final score that ranges from 0 to 10 (0 = normal = without symptoms, 1 = symptoms, 2 = severe symptoms). The three coinfection groups (9–21 dpi) had significantly higher scores than the HP-PRRSV and PCV2 groups. Among the coinfection groups, the HP-PRRSV/PCV2 group showed the highest score (see Additional file 1: Table S1 for details). (C) The average daily weight gain in the HP-PRRSV/PCV2 group was negative (14–21 dpi), whereas the gains of the other groups were positive. Error bars show the standard deviations. * indicates significantly higher or lower values. * p < 0.05, ** p < 0.01; and n.s., not significant.