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Abstract
AIM: To validate use of the electroencephalogram (EEG) and a minimal anaesthesia model for assessment of noxious sensory input caused by scoop dehorning of calves.
METHODS: Twenty Friesian heifers weighing 125–178 kg were maintained under light general anaesthesia using halothane and an established protocol (minimal anaesthesia model). They were then dehorned using a scoop dehorner either with (DH+LA) or without (DH) a lignocaine ring block, and changes in the EEG and electrocardiogram (ECG) recorded. Median frequency (F50), 95% spectral edge frequency (F95) and total power (Ptot) were derived from the EEG data.
RESULTS: There were significant increases in the F50 (p<0.01) and F95 (p<0.01), and a decrease in Ptot (p<0.01) following dehorning in the DH group, but there were no changes in the DH+LA group. Transient bradycardia in the first 75 sec following dehorning was recorded in the DH group compared with both pre-treatment values in the same group and with the DH+LA group (p<0.001). Tachycardia was evident by 15 min after dehorning in the DH but not the DH+LA group.
CONCLUSIONS: The results validate use of the EEG and a minimal anaesthesia model for assessment of noxious sensory inputs in cattle.
Acknowledgements
The authors are grateful for the joint funding of the study by the Ministry of Agriculture and Forestry of New Zealand and the Department of Environment, Food and Rural Affairs of the United Kingdom. The authors also thank all the members of the neurophysiological group, Massey University, for their help with experimental work and helpful discussion, and members of the Massey University Dairy Unit 1 for assistance during the experiment. TJ Gibson was the recipient of a C Alma Baker Postgraduate Scholarship.