Abstract
Beak trimming, the amputation of the anterior part of the
beak, is used to reduce feather pecking and cannibalism
amongst intensively reared poultry. This practice has
been criticized on the grounds that it may cause the bird
to suffer pain.
The approach adopted in this thesis towards the study of
pain perception in the chicken was to investigate the
possibility of peripheral neural phenomena which may be
related to acute and chronic pain sensation as a result of
beak trimming.
A review of the literature pertaining to the peripheral
neural basis of cutaneous sensation in birds revealed that
whilst mechanoreceptors and thermoreceptors are known to
be present in the avian beak, the evidence for nociceptors
has not been conclusive.
Acute electrophysiological techniques were employed to
study the primary afferent output from the beak, using a
preparation developed for this purpose. Cutaneous
nociceptors were discovered in the intact beak. An
analysis of their stimulus response characteristics
revealed many similarities with previously described
mammalian cutaneous nociceptors. It was considered that
the nociceptors would be activated during beak trimming,
and would transmit nociceptive information to the central
nervous system.
In the trimmed beak, the nociceptor population showed a
reduced sensitivity to heat. They therefore did not
provide a peripheral neural basis for hyperalgesia
following beak trimming.
Abnormal spontaneous afferent discharges were recorded
from the trimmed beak for up to 3 months following beak
trimming. These discharges have many similarities to
those resulting from peripheral nerve damage in mammals,
and they may have had a similar origin in neuromas.
It was concluded that the acute and chronic peripheral
neural consequences of beak trimming can be compared with
processes which can give rise to acute and chronic pain
sensations in man.
Further experiments are suggested to advance knowledge of
the possibility of pain perception in the domestic fowl.
