Some characteristics of brain electrical activity in the domestic chicken : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physiology at Massey University, Turitea, Palmerston North, New Zealand
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Date
2011
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Massey University
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Abstract
Studies in mammals have used measures of brain activity, such as the
electroencephalogram (EEG), to assess animal welfare. The aim here was to
determine whether the EEG could be used in a similar way in birds.
The effects of anaesthesia on the chicken EEG were relevant for later
studies on anaesthetised chickens. Therefore the effects of different
concentrations of four anaesthetics were recorded. The EEG was also used to
examine the development of brain activity in chicks with relevance to the onset
of consciousness. The EEG has been used to record responses to noxious
stimulation in anaesthetised mammals (i.e. without the animals experiencing
pain). To test this model in birds, anaesthetised chickens were exposed to
noxious stimuli as their EEG was recorded. The EEG response to decapitation
was also recorded in anaesthetised chickens to assess whether this is a suitable
method to use for killing chickens.
Halothane caused less suppression of brain activity than some of the other
agents, which suggests halothane would be a suitable agent to use in chicken
EEG studies. EEG first appeared on day 13 of the chick’s incubation, frequency
and amplitude increased until day 17. EEG activity decreased before hatching,
possibly due to an oxygen shortage in the egg. Consciousness seems unlikely
until after hatching. There did not seem to be any consistent change in the EEG
after noxious stimulation. This result contrasts with that found in mammals, and
may be due to differences in brain anatomy between the two species. It would be
worthwhile conducting further research to explore generators of the EEG and
pain processing in birds. After decapitation there were significant changes in the
EEG. The EEG also persisted for around 35 seconds following decapitation. This
may indicate that consciousness is not lost instantly at the time of decapitation
and that decapitation is an unsuitable method of killing chickens.
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Keywords
Consciousness in birds, Electroencephalography, Effects of anaesthesia, EEG responses, Chick development, Brain development, Decapitation