Comparison of analgesic techniques for antler removal in halothane-anaesthetized red deer (Cervus elaphus): cardiovascular and somatic responses.

OBJECTIVE

To compare changes in heart rate and arterial pressures resulting from compression of the antler pedicle or lidocaine 'ring block' and during subsequent antler removal during minimal halothane anaesthesia.

ANIMALS

Twenty-nine 2-year-old red deer (Cervus elaphus) stags, weighing 106-131 kg and carrying immature growing antler suitable for commercial harvest were studied.

MATERIALS AND METHODS

Anaesthesia was induced using intravenous propofol (median dose 8.0 mg kg(-1), range 5.2-11.0) and ketamine (median dose 2.2 mg kg(-1), range 1.9-2.4) and maintained using halothane in oxygen. End-tidal halothane concentration (Fe'HAL) end-tidal CO(2) tension (Pe'CO(2)), SpO(2), EEG, ECG, and direct systolic (SAP) mean (MAP) and diastolic (DAP) arterial pressures were recorded continuously. Respiratory rate and somatic responses were recorded. Baseline data were recorded once anaesthesia (Fe'HAL approximately 0.8%) was stable. Stags were randomly allocated to control, lidocaine 'ring block' or compression band treatment groups. One antler was removed 4 minutes after treatment. Cardiovascular responses to the application of analgesia and antler removal were analysed using a general estimates equation for repeated measures or area under the curve (AUC) analysis. Mean AUC was compared between groups using anova, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Somatic response data were compared with Fisher's exact chi-square test. A value of p < 0.05 was considered significant.

RESULTS

Heart rate fell during observations in all groups with no significant differences between groups. Arterial pressures in the control and lidocaine groups during treatment and removal were not different from baseline values or from each other. Compression group pressures were significantly higher than baseline during both treatment and removal. Compression group DAP and MAP were significantly higher after antler removal than during treatment. In control and lidocaine groups, the AUC for SAP, DAP, and MAP over the combined baseline, treatment, and removal period did not differ. The compression group AUC for DAP and MAP were significantly greater over the experimental period than both the lidocaine group and control groups. Somatic responses occurred in one animal at lidocaine injection and three at compression application. Somatic responses occurred in eight control animals and two in the compression group at antler removal. More animals responded to antler removal in the control group than in the compression (p = 0.015) or lidocaine (p < 0.001) groups.

CONCLUSIONS

Compression of the antler pedicle appears to be noxious. Pedicular compression is a less effective analgesic technique for antler removal compared to 'ring blocks' with lidocaine.

CLINICAL RELEVANCE

This study suggests that lidocaine 'ring blocks' are the current technique of choice for antler removal in deer.