Journal of Neuroscience Methods 201 (2011) 220–227 Contents lists available at ScienceDirect Journal of Neuroscience Methods j o ur nal homep age: www.elsevier.com/locate/jneumeth Development of mechanical and thermal nociceptive threshold testing devices in unrestrained birds (broiler chickens) B. Hothersall a,∗ , G. Caplen a , C.J. Nicol a , P.M. Taylor b , A.E. Waterman-Pearson a , C.A. Weeks a , J.C. Murrell a a School of Veterinary Sciences, University of Bristol, Langford, North Somerset BS40 5DU, UK b TopCat Metrology Ltd., Gravel Head Farm, Downham Common, Little Downham, Ely, Cambridgeshire CB6 2TY, UK a r t i c l e i n f o Article history: Received 15 June 2011 Received in revised form 26 July 2011 Accepted 30 July 2011 Keywords: Nociception Threshold testing Thermal Pain Broiler Chicken Welfare a b s t r a c t Behavioural signs of pain are difficult to quantify and interpret in animals. Nociceptive threshold testing is therefore a useful method for examining the perception and processing of noxious stimuli underlying pain states. Devices were developed to measure response thresholds to quantified, ramped mechanical and thermal nociceptive stimuli applied to the leg or keel of unrestrained birds. Up to 9 N mechanical force was delivered via a single round-ended 2 mm pin using a pneumatic actuator at 0.4 N s -1 . Heat was applied through a small copper element at 0.8 ◦ C s -1 to a maximum of 50 ◦ C. The repeatability and reliability of threshold measures were validated using 10–12 broiler chickens (aged 49–66 days) per site and modality. Mechanical threshold, or skin and threshold temperature, were recorded over three sessions across a 36 h period. Both stimulus types elicited clear, reproducible behavioural responses. Mechanical threshold means and 95% confidence intervals were 3.0 (2.8–3.2) N for keel and 2.0 (1.8–2.1) N for leg sites. Keel thermal tests gave a mean skin temperature of 39.3 (39.1–39.5) ◦ C, and threshold of 46.8 (46.6–47.1) ◦ C. Leg skin temperature was 35.7 (35.6–35.9) ◦ C and threshold 42.5 (42.2–42.8) ◦ C. Threshold measures were consistent within and across sessions and birds showed individual repeatability across tests within sessions. Individual birds’ mechanical keel thresholds were also repeatable across sessions. The apparatus gave reliable, reproducible measurements of thresholds to noxious mechanical and thermal stimuli. The range recorded was comparable with previously published nociceptor thresholds in dissected chicken nerve filament fibres, and the method appears suitable for studying nociceptive processes in broiler chickens. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction Assessment of pain in non-human species is challenging as pain comprises both subjective and emotional elements (IASP, 2004). In the absence of verbal reporting by the individual, pain can be inferred by their reactions (e.g. Le Bars et al., 2001). Nociception, the process of detecting actually or potentially damaging stimuli (Smith and Lewin, 2009) is more amenable to measurement. An understanding of nociceptive processing is fundamental to pain research, and has been advanced by the development in rodents of methods that define and examine behavioural responses to varying intensities of thermal or mechanical nociceptive stimuli (Hargreaves et al., 1988; Chaplan et al., 1994; McMullan et al., 2004). Nociception is also relevant to effective veterinary treatment ∗ Corresponding author at: School of Clinical Veterinary Science, Dolberry Build- ing, University of Bristol, Langford, North Somerset BS40 5DU, UK. Tel.: +44 01173319062. E-mail address: b.hothersall@bristol.ac.uk (B. Hothersall). and the assessment of animal welfare, and researchers have sought to improve clinical and practical relevance by adapting techniques to allow testing in unrestrained animals. Most such studies have focused on the effects of clinical disease conditions or analgesic drug administration on nociceptive thresholds in domesticated mammals (e.g. Whay et al., 1997; Robertson et al., 2003). Relative to baseline responses in healthy animals, decreases in mechanical threshold have demonstrated primary hyperalge- sia (sensitization of peripheral nociceptors) at the site of a wound (Lascelles et al., 1998) and at the site of experimentally induced inflammation (Sandercock et al., 2009). Mechanical nociceptive threshold testing devices have also been used to show secondary hyperalgesia, in association with foot disease in cattle (Whay et al., 1997, 1998) and post-operatively in dogs (Lascelles et al., 1998). Sheep with foot rot displayed decreased mechanical threshold at the lower radius but thermal thresholds at the pinna were unaltered (Ley et al., 1989). In contrast, Welsh and Nolan (1995) reported decreased thermal threshold on the ear pinna following laparotomy in sheep, whereas mechanical threshold at the radius was unaffected. Secondary hyperalgesia to a noxious stimulus 0165-0270/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2011.07.028