Effects of beak trimming and restraint on heart rate, food intake, body weight and egg production in hens

1. Heart rate (measured on restrained hens in two experiments) was used as an indicator of short term fear and pain responses of light and heavy strains of hens subjected to beak trimming. 2. In the first experiment 3 mm of the upper and lower mandibles was trimmed, while in the second 0, 2, 4, 6 and 8 mm of upper and lower mandibles were removed. 3. Production responses to beak trimming were measured after trimming, for 4 weeks in experiment 1 and for 10 weeks in experiment 2. 4. In the first experiment the recovery of beak trimmed hens to normal heart rate took significantly longer than that of control hens subjected only to catching and restraint, suggesting that there was short term pain associated with beak trimming. 5. The heavier strain took about 4 min longer to return to a normal heart rate than the lighter strain, indicating a strain difference in responsiveness to beak trimming. 6. Trimming the hens' beak by 3 mm had no significant effect on rate of lay or body weight, but their mean egg weight was depressed and food intake took 9 to 10 d to recover to pre-trimming values. 7. In the second experiment a plateau was reached in recovery time of the heart rate once 4 mm of beak was removed. Removal of 4, 6 and 8 mm of beak depressed normal feeding and resulted in variable effects on production and body weight.