Thermal nociception as a measure of non-steroidal anti-inflammatory drug effectiveness in broiler chickens with articular pain

Pain associated with poultry lameness is poorly understood. The anti-nociceptive properties of two nonsteroidal anti-inflammatory drugs (NSAIDs) were evaluated using threshold testing in combination with an acute inflammatory arthropathy model. Broilers were tested in six groups (n = 8 per group). Each group underwent a treatment (saline, meloxicam (3 or 5 mg/kg) or carprofen (15 or 25 mg/kg)) and a procedure(Induced (arthropathy-induction) or sham (sham-handling)) prior to testing. Induced groups had Freund’s complete adjuvant injected intra-articularly into the left intertarsal joint (hock). A ramped thermal stimulus (1 C/s) was applied to the skin of the left metatarsal. Data were analysed using random intercept multi-level models.Saline-induced birds had a significantly higher skin temperature (± SD) than saline-sham birds(37.6 ± 0.8 C vs. 36.5 ± 0.5 C; Z = 3.47, P < 0.001), consistent with an inflammatory response. Salinewas associated with significantly lower thermal thresholds (TT) than analgesic treatment (meloxicam:Z = 2.72, P = 0.007; carprofen: Z = 2.58, P = 0.010) in induced birds. Saline-induced birds also had significantlylower TT than saline-sham birds (Z = 2.17, P = 0.030). This study found direct evidence of an associationbetween inflammatory arthropathies and thermal hyperalgesia, and showed that NSAIDtreatment maintained baseline thermal sensitivity (via anti-nociception). Quantification of nociceptiveresponsiveness in a predictable broiler pain model identified thermal anti-hyperalgesic properties oftwo NSAIDs, which suggested that therapeutically effective treatment was provided at the doses administered.Such validation of analgesic strategies will increase the understanding of pain associated withspecific natural broiler lameness types. 2013 The Authors. Published by Elsevier Ltd. All rights reserved.