ABSTRACT: Routine removal of the tip of the beak
of chickens within the poultry industry leads to changes
in pecking behavior, which have previously been
interpreted as being indicative of pain. By analyzing
the force of pecks, with and without the topical application
of an analgesic to the beak, we investigated
if changes in pecking behavior were due to a loss of
sensitivity in the beak or were pain related. Pecking
behavior was compared between intact-beak and beaktrimmed
chicks with or without topical application of
lignocaine during a pain-free period (within 24 h of
beak trimming) or after this period (d 2 to 9 of age).
After pecking behavior tests, chicks were trained to use
a magnetic stimulus to locate hidden food in 1 corner
of a square arena. In unrewarded magnetic tests, the
location of the chick relative to the magnetic stimulus
was determined by automatic image recognition.
Beak-trimmed chicks pecked harder than intact-beak
chicks within 24 h of beak trimming (P = 0.04), possibly
as a means of compensating for the loss of sensory
feedback in beak-trimmed chicks. At 2 to 9 d of age,
beak-trimmed chicks took longer to peck the pecking
stimulus (P < 0.001) and showed fewer pecks in total
(P < 0.001), suggesting a reduced pecking motivation.
The force of pecks, however, did not differ among treatments
at 2 to 9 d of age, suggesting that beak-trimmed
chicks were not experiencing pain from the beak. In the
magnetic tests, hungry intact-beak chicks stayed nearer
to the magnetic stimulus (P = 0.005) and spent proportionally
more time within 125 mm of the magnetic
stimulus (P = 0.02) that had previously been associated
with food than beak-trimmed chicks, which indicated
that intact-beak birds were better able to detect
the magnetic stimulus than beak-trimmed birds. We
concluded that minor beak trimming at a young age
did not result in pain in young domestic chicks, but instead
led to impaired function of the magnetoreceptors
and mechanoreceptors of the beak.