Minor beak trimming in chickens leads to loss of mechanoreception and magnetoreception1

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 beak-trimmed 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.