Electrophysiological investigation of the effects of beak trimming in the domestic fowl (gallus gallus domesticus)

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.