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

Abstract

Six flocks of laying hens were housed in percheries at each of four stocking densities (6, 14, 22 or 30 birds m −2) from 14 to 30 weeks of age. Stocking density was manipulated by changes in flock size (72, 168, 264 or 368 birds) 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, and 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 age. 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 flock size and stocking density. Mild feather pecking increased with bird age and was most frequently observed on the perchery floor although, at higher flock sizes and stocking densities, it also occurred on the perches. Severe feather pecking was infrequent, especially at the lower flock sizes and stocking densities, but was most likely to occur near the nest boxes. Vent pecking was extremely rare. Aggressive pecking was most common in the smaller flocks at the lowest stocking densities, possibly because these birds attempted to form social hierarchies. Birds in the larger flocks at higher densities appeared to adopt non-social, non-aggressive behavioural strategies.