RESEARCH PAPER Do psychological and physiological stressors alter the acute pain response to castration and tail docking in lambs? Corinna Clark, Mike Mendl, Jennifer Jamieson, Ashleigh Arnone, Avril Waterman-Pearson & Joanna Murrell Department of Clinical Veterinary Science, University of Bristol, Langford, North Somerset, UK Correspondence: Joanna Murrell, Department of Clinical Veterinary Science, University of Bristol, Langford House, Langford, North Somerset BS40 5DU, UK. E-mail: jo.murrell@bristol.ac.uk Abstract Objective To investigate whether events that may be stressful to young lambs, including simulated infection or social isolation, modulate pain experi- enced by lambs following castration and tail dock- ing (C/D). Study design Randomised, controlled, prospective study. Animals Fifty male lambs born to 46 second-parity Mule ewes. Methods Lambs were allocated randomly to one of four groups, experiencing either a potential stressor or handling on day 2 after birth, followed by C/D or handling only on day 3. Quantitative sensory testing (QST) data [mechanical nociceptive thresholds (MNT), Semmes Weinstein filaments (SW), response to cold] and serum cortisol concentration were measured at time points after application of treat- ments to lambs on days 2 and 3 after birth. The treatment groups were LPS, injection of bacterial lipopolysaccharide IV on day 2, C/D on day 3; ISOL, isolation from the dam for 10 minutes on day 2, C/D on day 3; CAST, handling only on day 2, C/D on day 3; CONT, handled only on days 2 and 3. Results Castration and tail docking caused transient hypoalgesia as measured by MNT and SW. Simu- lated infection and isolation caused hyperalgesia 3 hours after application, indicated by a reduction in MNT, however they did not alter the pain response to C/D compared to lambs in the CAST group. Injection of LPS and C/D caused increased serum cortisol concentration. The magnitude of the cortisol response to C/D was not altered by prior exposure to either LPS or isolation. Conclusions and clinical relevance LPS and isola- tion did not modulate the response to C/D but did cause hyperalgesia. This highlights the importance of flock health management and husbandry tech- niques to reduce the incidence of either systemic infection or psychological stressors in young lambs. Keywords castration, isolation, lambs, lipopolysac- charide, nociceptive thresholds. Introduction Castration and/or tail docking of lambs currently is routine husbandry practice within the UK sheep industry (FAWC 2008) and, in the UK, can be carried out on lambs up to 7 days of age using the rubber ring (elastration) method without concur- rent provision of analgesia (FAWC 2008). Reasons for the routine castration of male lambs include: concern about a reduction in meat quality and therefore price reduction; prevention of indiscrimi- nate breeding; and an increased risk of injury through fighting as dominance is established and maintained. The Code of Recommendations for the Welfare of Livestock: Sheep (DEFRA 2003) recommends that 134 Veterinary Anaesthesia and Analgesia, 2011, 38, 134–145 doi:10.1111/j.1467-2995.2011.00594.x