Electroencephalographic responses of calves to the noxious sensory input of slaughter by ventral neck incision and its modulation with non-penetrative captive bolt stunning : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Physiology, Massey University, Palmerston North, New Zealand
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Date
2009
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Massey University
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Abstract
Slaughter by ventral neck incision (VNI) is performed on some animals
without prior stunning in New Zealand and other countries. A single incision with a
razor sharp blade is made in the ventral aspect of the neck, sectioning both carotid
arteries and jugular veins, though, not the vertebral arteries. There are a number of
potential welfare concerns surrounding slaughter by VNI including pain due to the
incision, which may lead to distress during the time before loss of consciousness. The
aims of this thesis were to identify cortical responses indicative of noxious stimulation
due to slaughter by VNI using analysis of the electroencephalogram (EEG) power
spectrum and to investigate the effects of non-penetrative captive bolt (NPCB)
stunning on these cortical responses.
The studies utilised adaptations of a minimal anaesthesia model, which has
been validated in a range of mammalian species. Surgical dehorning was used as a
validation technique for this methodology in cattle and demonstrated a ‘typical’ EEG
response to noxious stimulation. Cattle slaughtered by VNI without prior stunning
produced specific responses in the EEG that strongly indicated responses to noxious
stimulation. Causation was investigated in cattle where blood flow through the brain
remained intact during neck tissue incision (NTI) or the major blood vessels of the
neck were isolated and transected independently of other neck tissues (BVT). The
response to neck incision in intact animals was principally due to the noxious sensory
input due to incision of neck tissues and not mainly as a result of loss of blood flow
through the brain. NPCB stunning produced states of cortical activity that were
incompatible with the maintenance of sensibility and pain perception. Experimental
examination of the time to onset of undoubted insensibility was attempted in cattle
subsequent to a pilot study in sheep. The generation of somatosensory-evoked
potentials was problematic in cattle.
The conclusions of this thesis are that incision of neck tissues during slaughter
without prior stunning constitutes a substantial noxious stimulus. Were an animal
conscious, this stimulus would be perceived as painful until the onset of hypoxiainduced
insensibility. This would represent a significant compromise to animal
welfare.
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Keywords
Animal stress, Cattle slaughter, Cortical response, Pain perception, Pain in animals