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Doctoral thesis, 2000

Feather pecking in laying hens : social and developmental factors

Bilcik, Boris


The relationship between pecks received by individual birds and the feather and skin damage of those birds was examined. The social factor investigated was group size and the development of feather pecking and feather damage was followed. Laying hens were raised in floor pens in group sizes of 15, 30, 60 and 120 birds and at four different ages detailed feather scoring and behavioural observations were carried out. Feather condition was worse in larger group sizes, with the largest difference for the group of 120 birds. Severe feather pecks were found to be strongly related both to feather damage and skin injuries. The body parts that received most pecks were the tail, rump and back, but most quickly denuded body part was the belly. The number of received aggressive pecks (but not gentle or severe feather pecks) was negatively related to body weight.

The connection between pecking at feathers and pecking at the ground in individual birds was studied. The same experimental setup was used as in the first part of the thesis with the same four group sizes. The results showed that most feather pecking activity occurred in the largest group size (120 birds) and there was some evidence of an increasing frequency of aggressive pecks received with increasing group size. The parts ofthe body which were targets for feather pecking varied depending on the location ofthe bird giving the peck and the bird receiving it. When looking at the behaviour of individuals, birds doing a lot of feather pecking also showed more ground pecking supporting previous work that feather pecking individuals are generally more active.

The prediction that more feather pecking in larger groups together with increased competition between birds may be associated with greater fearfulness was investigated. Tonic immobility duration of laying hens kept in groups of different sizes and tested in both their home pen and in temporary isolation in a separate room was studied. Tonic immobility increased with group size, with a significant difference between group sizes 15 and 120, suggesting that larger group size is connected with increased fearfulness. Some methodological considerations are made concerning the testing in the home environment ofthe hen.

The possibility of using individual differences in dopaminergic sensitivity (estimated by the behavioural response to apomorphine in chicks shortly after hatching) to test for susceptibility to become a feather pecker as an adult was examined. Apomorphine treatment caused increased motor and pecking activities with large individual variation, however, there was no correlation between the behaviour of young chicks after the apomorphine challenge and their feather pecking behaviour as adult birds. Using quantitative autoradiography, the differences between feather peckers and non-peckers in dopamine DI and D2 receptor densities in the basal forebrain were measured. There was no significant difference in DI or D2 receptor densities in the whole lobus parolfactorius (LPO) or paleostriatum augmentatum (PA), however, there were minor alterations in densities in distinct sections in rostral (increased DI in peckers in LPO), medial (increased D2 in peckers in PA) and caudal region (increased D2 in non-peckers in LPO).


laying hens; poultry behaviour; feather pecking; feather scoring; tonic immobility; apomorphine; dopamine receptors; group size; plumage condition

Published in

Acta Universitatis Agriculturae Sueciae. Veterinaria
2000, number: 82
ISBN: 91-576-5934-6
Publisher: Swedish University of Agricultural Sciences

    UKÄ Subject classification

    Animal and Dairy Science

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