Electroencephalographic responses of halothane-anaesthetised calves to slaughter by ventral-neck incision without prior stunning

Abstract

AIM: To investigate whether the electroencephalographic (EEG) responses to slaughter by ventral-neck incision without prior stunning may be perceived as painful in halothane-anaesthetised calves.

METHODS: Fourteen Angus steers were minimally anaesthetised with halothane, using an established anaesthesia protocol. EEG indices were recorded bilaterally for 5 minutes prior to and 5 minutes following ventral-neck incision. A single incision was made in the ventral aspect of the neck, severing all tissues ventral to the vertebral column including the major blood vessels supplying and draining the head. Changes in the median frequency (F50), 95% spectral edge frequency (F95) and total power of the EEG (Ptot) were used to investigate the effects of ventral-neck incision. At the completion of the experiment, brains of calves were examined histologically.

RESULTS: During the 30 seconds following ventral-neck incision, the F95 and Ptot showed signifi cant changes (p<0.05) compared with pre-treatment values. The F50 increased significantly from recordings from the right side of the cranium. No gross or histological abnormalities were detected in the brains following slaughter.

CONCLUSIONS: This study is the fi rst investigation of the noxiousness of slaughter by ventral-neck incision, using EEG spectral analysis. It demonstrated that there is a period following slaughter where ventral-neck incision represents a noxious stimulus.

KEY WORDS:

• Calves
• compressed spectral array
• electroencephalogram
• emergency slaughter
• minimal anaesthesia
• nociception
• pain
• slaughter
• ventral-neck incision

Acknowledgement

The authors would like to thank the members of the Comparative Neuroscience Group, the Large Animal Teaching Unit, and the Small Animal Production Unit, Massey University, for assistance during the experiment. This study was jointly funded by the Department for Environment, Food and Rural Affairs of the United Kingdom and the Ministry of Agriculture and Forestry of New Zealand. TJ Gibson was the recipient of a C Alma Baker Postgraduate Scholarship.