The effect of LPS and ketoprofen on social behaviour and brain physiology in group housed pigs

Poor health is a risk factor for tail biting but the mechanism behind this link is still unclear. An injection with lipopolysaccharide (LPS) can be used to model aspects of sickness. Recent studies showed more tail- and ear- directed behaviour in LPS injected pigs compared to saline injected pigs. The aim of this study was to evaluate social behaviour and stress physiology of pigs after LPS injection [1.2 µg/kg], and to test the effect of a nonsteroidal anti-inflammatory drug (NSAID) on the effects of LPS. The experiment was approved by the national animal research authority (FOTS id 15232). Fifty-two female pigs (11-12 weeks) were randomly allocated to four treatments all comprising two injections: Saline-Saline (SS), Saline-LPS (SL), Ketoprofen-Saline (KS), Ketoprofen-LPS (KL). The first substance was administered intramuscularly (i.m.). The latter was administered intravenously (i.v.) on average 60 ± 14 min afterwards in an ear vein during fixation with a mouth snare. Pigs were marked on the back for individual identification and video recorded. Activity was scan sampled every 5 min for 6 h after the last i.v. injection in the pen. Social behaviour was observed continuously in 10 x 15 min intervals between 8 am and 5 pm at baseline and one and two days after i.v. injection with focus on ear and tail exploration as well as manipulation of other body parts. Data were analysed by a mixed model to account for repeated measures and baseline behaviour. Saliva was sampled at baseline and at 4, 24, 48, 72 h after the i.v. injection and analysed for cortisol. Salivary cortisol was significantly higher in SL pigs (1067.6 ± 77.8 pg/ml) compared to KL pigs (641.4 ± 77.8 pg/ml; student’s t-test: p < 0.001), SS pigs (418.0 ± 84.6 pg/ml; p < 0.001) and KS pigs (258.0 ± 77.8 pg/ml; p < 0.001) at 4 h post injection (F(treatment*time point)12,182.8 = 4.65; p < 0.001). SL pigs showed more sternal recumbancy (296 counts) and were less active (52) than SS pigs (lying inactive sternal: 149 | active: 186, student’s t-test for both models respectively: p < 0.001), KL pigs (174 | 217, p < 0.001), and KS pigs (151 | 215, p < 0.001) during 6 h post injection (lying inactive sternal F(treatment)3,48 = 9.26; p < 0.001; active F(treatment)3,48 = 14.66; p < 0.001). Treatment effects on social behaviour were not consistent. SL pigs performed longer ear exploration (sum per day: 1702.0 s) than SS pigs (465.9 s) two days after i.v. injection, (student’s t-test: p = 0.02; F(treatment*day)6,88 = 1.49, p = 0.19). They did not differ at baseline. The duration of tail exploration (F(treatment*day)6, 87.58 = 0.23, p = 0.97) and manipulation of other body parts (F(treatment*day)6, 88 = 0.36, p = 0.90) did not differ between treatments. LPS activated the HPA-axis (measured 4 h after injection) and elicited so-called sickness behaviour within 6 h after injection as indicated by lower activity in LPS injected pigs.