Kells, N. J., Beausoleil, N. J., Godfrey, A. J. R. et al. 2020. Effect of analgesic strategies on pain behaviour associated with combined ring castration and hot iron tail docking in Merino lambs. Applied Animal Behaviour Science 222, 104914.
Most countries don’t require analgesia to be provided to lambs <6 months of age undergoing castration and tail-docking. However, increasing concern for the welfare of farmed livestock means that analgesia is likely to be mandatory at all ages in the future. We investigated whether prior administration of local anaesthesia (LA), alone or in combination with a systemic non-steroidal anti-inflammatory drug (meloxicam), reduced behavioural indicators of pain in 4–6-week-old New Zealand Merino lambs following ring castration and hot iron docking. Ninety singleton male lambs were randomly allocated to one of six treatment groups: sham castration and docking (C/D) (SHAM); C/D without analgesia (CON); C/D with LA (LA); C/D with systemic meloxicam (MEL); C/D with LA and meloxicam administered separately (LA + M); or C/D with LA and meloxicam mixed and administered together (LAM). Pain behaviours were scored continuously during three 30-minute periods prior to (period A), shortly after (15–45 min; Period B), and 4 h (Period C) after treatment. Significant treatment x period interactions were identified for proportions of time spent normal standing/walking (P < 0.001), abnormal/standing walking (P = 0.002) and twisted lying (P < 0.001), and the frequency of foot kicks/stamps (P < 0.001), turns to hindquarters (P = 0.025), restlessness (P < 0.001), hindlimb stretches (P < 0.001) and tail lifts (P < 0.001). CON lambs spent more time standing/walking abnormally and twisted lying and less time standing/walking normally in Period B, relative to Period A and relative to SHAM lambs. CON lambs also exhibited higher frequencies of foot stamp/kicks, restlessness, turns to hindquarters, hindlimb stretches and tail lifts than SHAM lambs in Period B. All behaviours returned to pre-treatment values in Period C. Prior administration of LA, alone or with meloxicam, reduced the time spent twisted lying and the frequency of hindlimb stretching and tail lifting in Period B but did not influence other pain-related behaviours. Meloxicam alone had no effect on pain behaviour in any period. Due to the short duration of behavioural responses and the limited analgesic effects observed, the efficacy of the novel mixture of LA and meloxicam relative to LA and meloxicam administered separately could not be established. There appeared to be no deleterious effects to combining the two agents for quicker administration. In conclusion, prior administration of LA reduced the acute pain associated with ring castration and hot iron docking to some degree. Further research is required to determine an optimal analgesic strategy for reducing pain associated with ring castration and hot iron docking in Merino lambs.