Late-Breaking: Acute Endotoxinemia May Increase Intercostal Temporary Mechanical Nociception in Wethers

Abstract Systemic inflammation induced by lipopolysaccharide (LPS; endotoxin) is associated with generalized hyperalgesia in humans and some animal models. However, the effects of endotoxin-induced inflammation on pain threshold in livestock, such as sheep, is unknown. Eight wethers [~1 year of age; 61.3 ± 0.5 kg BW] were administered saline (2 mL; n = 4) or endotoxin (2 mL; 400 ng of LPS / kg BW; n = 4) intravenously. A handheld algometric unit was used to administer temporary mechanical nociception (TMN) before (Day -2) and after (Day 1) treatment administration by the same person three times at two locations on the right thorax (intercostal spaces 6 and 9). Two-way ANOVA was completed in SAS v9.4 (Cary, NC). There were effects of day (P < 0.001) and location (P < 0.0001) on TMN, such that the force needed to induce TMN on Day -2 (2.04 +/- 0.15 kgF) was less than on Day 1 (2.93 +/- 0.15 kgF) and the force needed to induce TMN at intercostal space 6 (1.81 +/- 0.15 kgF) was less than at intercostal space 9 (3.15 +/- 0.15 kgF). While there was no effect of treatment (P = 0.96), or interaction of treatment and location (P = 0.19), day and location (P = 0.25), or treatment and day and location (P = 0.49), there was a tendency for an interaction of treatment and day (P = 0.06), such that TMN was not different on Day 1 (2.73 +/- 0.30 kgF) and Day -2 (2.24 +/- 0.30 kgF) for animals receiving saline but was greater on Day 1 (3.12 +/- 0.30 kgF) than Day -2 (1.83 +/- 0.30 kgF) for animals receiving LPS. While systemic inflammation is associated with reduced pain threshold in some models, acute LPS-induced inflammation may increase intercostal TMN in castrated sheep.