Lipopolysaccharide-induced sickness behavior in pigs is inhibited by pretreatment with indomethacin

Many of the behavioral responses following acute bacterial or viral infection are now considered important for maintaining homeostasis during inflammation. In the present study, we extend this concept to pigs (16 crossbred barrows) by demonstrating that lipopolysaccharide (LPS, .5, 5, or 50 micrograms/kg BW) from Escherichia coli injected i.p. reduces feed intake, decreases activity, and elevates body temperature. To determine whether any of these effects could be mediated via a prostaglandin (PG)-dependent mechanism, a second experiment with 16 crossbred barrows was conducted. Barrows were pretreated with indomethacin (IND, 5 mg/kg BW [a cyclooxygenase inhibitor]), and their behavior and body temperature following a challenge i.p. injection of LPS (5 micrograms/kg BW) were assessed. Pretreatment with IND inhibited the anorexia and inactivity caused by LPS, suggesting that the behavioral effects of LPS are dependent on activation of a PG system. Lipopolysaccharide alone, however, did not elevate body temperature in this case; thus, the involvement of PGs in this response was not determined. Collectively, these data indicate that pigs respond to LPS by reducing feed intake, decreasing activity, and becoming febrile. The ability of IND to inhibit behavioral effects of LPS is consistent with the hypothesis that a PG system is involved in mediating sickness behavior. Perhaps, by altering the activity of cyclooxygenase it is possible to enhance or inhibit the behavioral symptoms of sickness in pigs.