Behaviour of pigs with viral and bacterial pneumonia

The behavioural response to infection is well organized and may enhance disease resistance and facilitate recovery, but the behaviour of pigs with an acute respiratory infection has not been assessed. Therefore, the purpose of this study was to evaluate behaviour of pigs inoculated with Mycoplasma hyopneumoniae (Mh) and porcine reproductive and respiratory syndrome virus (PRRSV). Sixty-four pigs were subjected to one of four treatment combinations (2 × 2 factorial) of Mh (inoculated at 4 weeks of age) and PRRSV (inoculated at 6 weeks of age). The four treatments were (1) control, (2) inoculation with Mh, (3) inoculation with PRRSV, and (4) inoculation with both Mh and PRRSV. One-half of the pigs from each treatment were killed 7 days after PRRSV inoculation for purposes unrelated to this study and hence were not used for behavioural analysis. Pigs that were included were video recorded during the 18 h light phase for 13 days beginning the day of PRRSV inoculation. Food intake and time spent feeding, active (standing, including walking, sitting, or feeding) and lying were determined. When pigs were lying a determination was made as to whether they were lying ventrally or laterally, and in contact with a penmate. Body temperature was measured 7 and 14 days after PRRSV inoculation. After inoculation with PRRSV, there was no significant main effect of Mh or interaction between Mh and PRRSV for food intake, body temperature, or any behaviour measured. Thus, the four treatments were pooled to form two treatments designated PRRSV negative (control and Mh; PRRSV−) and PRRSV positive (PRRSV and Mh with PRRSV; PRRSV+) and analyzed. Each day after PRRSV inoculation, PRRSV+ pigs spent less time (P = 0.005) feeding compared to PRRSV− pigs, and the decrease in feeding time was associated with a decrease in food intake (P < 0.001). PRRSV+ pigs decreased (P < 0.001) activity after inoculation with PRRSV compared to PRRSV− pigs and the amount of time spent lying was greater (P < 0.001) in PRRSV+ pigs compared to PRRSV− pigs. Furthermore, PRRSV+ pigs spent more of their total lying time in a ventral position (P = 0.06) and in contact with a penmate (P < 0.001) compared to PRRSV− pigs. Body temperature was increased (P < 0.001) in PRRSV+ pigs 7 days after PRRSV inoculation. Since sickness behaviour and fever are adaptive responses to infection, these data indicate that pigs with an acute PRRSV infection evoke a behavioural strategy that may support recovery.