Differential effects of increased stocking density, mediated by increased flock size, on feather pecking and aggression in laying hens

Six flocks of laying hens were housed in percheries at each of four stockin g densities (6, 14, 22 or 30 birds m(-2)) from 14 to 30 weeks of age. Stock ing density was manipulated by changes in nock size (72, 168, 264 or 368 bi rds) within percheries of the same floor and height dimensions. The pecking behaviour of birds was observed directly at 15, 22 and 30 weeks of age, an d corrected for the number of birds in view. Egg production was recorded at 23 and 27 weeks of age, and plumage condition was scored at 30 weeks of ag e. At 23 weeks of age, egg production was greater at 6 birds m(-2) than at other stocking densities. The plumage condition of the birds was best at 6 birds m-2 and worsened with increased flock size and stocking density. The behavioural observations suggested that this was due to an increase in mild feather pecking with increased nock size and stocking density. Mild feathe r pecking increased with bird age and was most frequently observed on the p erchery floor although, at higher flock sizes and stocking densities, it al so occurred on the perches. Severe feather pecking was infrequent, especial ly at the lower flock sizes and stocking densities, but was most likely to occur near the nest boxes. Vent pecking was extremely rare. Aggressive peck ing was most common in the smaller flocks at the lowest stocking densities, possibly because these birds attempted to form social hierarchies. Birds i n the larger nocks at higher densities appeared to adopt non-social, non-ag gressive behavioural strategies. (C) 1999 Elsevier Science B.V. All rights reserved.